Now Do It Again Backwards

"Kim: The alien said that if I recreate the conditions of the accident and fly into the timestream, there's a chance I might be able to get back into my reality. Paris: Might? Kim: He couldn't give me any guarantees."

- Star Trek: Voyager, "Non Sequitur"

Come on in. Sit down. Aw, there's no need to be nervous. We all know how it is out there. Sometimes things get out of hand. Now, you just tell me all about it. I've heard it all before. Maybe you flew your spaceship through a wormhole while your engine was leaking, and you ended up in a parallel universe. Perhaps you are a gang of super heroes and you've had a bit of a whoopsie with some Applied Phlebotinum, some Green Rocks, and a liquid lunch. Maybe you fell back through time or ended up in an alternate dimension, or perhaps you just got zapped by some weird space anomaly.

Well, have no fear. We can help you. Whatever ill effects you've suffered, they can all be fixed by just doing the same thing that caused the problem, but in reverse. Fly back through the wormhole without fixing your engines first. Stand in the same place as before and rub the Applied Phlebotinum on the Green Rocks again. Find the hole in spacetime that leads back to the future or your home dimension, or go get zapped by the same anomaly (though you might want to Reverse Polarity first before you do that last one).

A subtrope of the Reset Button. Sometimes you can even deal with magical or even memory issues in much the same way—by repeating the spell (or blow to the head) backwards.

Compare Traumatic Toggle, where it's the repetition, not the reversal, that does the trick.

Now, about payment...

Anime And Manga

 * Fullmetal Alchemist (manga/Brotherhood): Edward Elric lost his arm in exchange for bonding his brother Alphonse's soul to a suit of armor.

Comic Books

 * In The Essential Silver Surfer the Surfer goes into the future by accelerating to near-lightspeed. He returns to the present by doing the same in the other direction.
 * Captain Carrot and His Amazing Zoo Crew escaped from a black hole by flying their rocketship through it backwards. No points for asking how it's possible to fly a rocketship backwards in the first place. Justified, since this is Earth-C, the cartoon dimension, which is supposed to have cartoon physics.
 * In The Incredible Hulk, Banner's Girlfriend Of The Week, Kate Waynesboro, gets dumped into some wacky gizmo and comes out the other end as an evil, female version of MODOK, complete with giant head and hoverchair. Naturally, sending her through the machine again backwards returns her to normal.

Film

 * ''The Incredible Mr. Limpet". The method Admiral Spewter suggests to turn Henry Limpet back into a human being.
 * Frankenstein Meets The Wolf Man (1943). Dr. Frankenstein's journal explains that the practically immortal monster can be killed by attaching him to the machine that gave him life and "changing the poles" (AKA reversing the polarity).
 * Subverted hard in Drag Me to Hell:
 * Wee Sing in the Big Rock Candy Mountains: After the characters perform "Follow Me," the Snoodle-doodles ask them to "do it all backwards, really fast!" They do it.
 * In the Disney Channel movie "Halloweentown 2: Calibar's Revenge", the villain put a spell on Halloweentown's denizens, making them gray and boring, and the only way to reverse it is to say the spell backwards. They can't find Aggie's spellbook, so they don't even know what the spell is, but Marnie accidentally figures it out when she was "trap a" in a sentence: the original spell was "apart".

Literature

 * In Stephen King's The Langoliers, the characters accidentally pass through what they dub a "time-rip". The solution to getting back where they belong? Fly back through the time-rip from the other direction (the trip was west-to-east, the return east-to-west).
 * The trick to this, of course, is that everyone had to be asleep when they hit the time rip, or else they'd disappear like the rest of the people on the plane the first time through.
 * There is an alternate theory that those people didn't disappear, they simply remained in the present. Or, rather, were moved forward to the new present, while everyone asleep got stuck in the old present. Of course, without a plane, their outlook wasn't very good...
 * Robert Heinlein novel Starman Jones. Starships travel by accelerating to near lightspeed and making a "transition" to a new location. During one transition a mistake is made and the ship ends up lost. The crew tries to get back by returning to the point where they appeared and making a transition which is the reverse of the original in the hope that it will take them home.

Live Action TV

 * Star Trek was likely the worst offender in this case. The initial example above was from the Star Trek: Deep Space Nine episode "Crossover", and the quote comes from the Star Trek: Voyager episode "Non Sequitur". A list of all the occurrences of this trope in Star Trek turned out to be longer than the Universe and collapsed into a black hole that we were only barely able to reverse by rewriting the list in reverse order, so let's just leave it at those two.
 * An episode of the kids TV show Space Cases featured Harlan Band (and the console that could inform the crew of the lethal radiation leak) becoming invisible after getting zapped by a discharge from the Christa's engine core (which only happened because he spilled juice on it). The obvious solution was to have him stand in the same place, have the ship's android pour more juice on the engine core, and, of course, Reverse the Polarity of the neutron flow.
 * Annoyingly enough, the Stargate SG-1 episode "1969" (one of its most Trekish episodes ever, along with such gems as "Emancipation" and "Brief Candle"). Slightly subverted as they return to the future, not to the point in time from which they departed, and Cassandra has to send them back in time from there.
 * Also done in "Ripple Effect" where to return the dozens of alternate SG-1's to their home dimensions, they repeat the event that started the whole mess, and send them back through the gate in reverse order of when they arrived.
 * Also pops up in an episode of Atlantis, "The Daedalus Variations", where in order to get back to their own reality, Sheppard and the team have to fly the alternate reality Daedalus back through all the other parallel realities encountered during the episode in reverse order.
 * In the episode of Farscape, "The Locket," they fly into some mist where time flows differently, and they discover that hundreds of years have passed in the few hours they were in it. They don't seem to be able to get out until they... fly backwards out of it and this reverses time to right before they entered it.
 * Subverted in an early episode where the crew plans to use reverse thrust to get out of an alternate dimension (since they were going forward when they punctured the other reality) but are told that they will completely destroy the dimensional barrier if they try to back out. They have to go forward instead and count on the extra dimensional being charged with repairing the rift to guide them through safely.
 * Red Dwarf "Angels and Demons". This is how Kryten reconstitutes the RD from its triplicator-created Light and Dark copies.
 * Subverted in an episode of Boy Meets World. An accident with a microwave oven throws Corey back to the 1950s, and a Wise Old Man tells him that to get back, he just needs to recreate the circumstances of the accident. There's just one problem, as Corey points out: there were no microwave ovens in the 1950s. Luckily for Corey, it was All Just a Dream.
 * Actually there were. The first commericial microwave oven was manufactured in 1947, and a home version went on sale in 1955.
 * In The Twilight Zone episode 'The Odyssey of Flight 33', the plane flies into an effect that puts them into the Jurassic period. They return to the effect and instead end up 30 years before their own time. The episode ends with them low on fuel and heading for the effect once more.

Theatre

 * In The Complete Works of William Shakespeare, the players do Hamlet...backwards.

Tabletop RPG

 * Call of Cthulhu (tabletop game) spells.
 * When the Resurrection spell is spoken in reverse, it will cause a resurrected creature to return to dust.
 * Based on Lovecraft's
 * Adventure Shadows of Yog-Sothoth. If the spell that's being used to raise R'lyeh is cast in reverse, it will cause R'lyeh to sink again.
 * In early editions of Dungeons & Dragons some spells were reversible and casting the reverse of a spell could negate the normal version.
 * Flesh to Stone/Stone to Flesh
 * Neutralize Poison/Poison
 * Bless/Curse
 * There are also a few magical effects that will undo themselves if applied a second time, like the (cursed) Helm of Opposite Alignment (as long as you didn't start with an alignment that was neutral on either axis) or Belt of Masculinity/Femininity, although in those two cases the character would need to go find a new copy, as each item discharges and loses its magic when used.
 * The Truenamer, if it were playable, would have this mechanic for some of its Utterances (i.e., spells): you can say them backwards to achieve the opposite of the normal effect.

Video Games

 * The infamous plasma corridor in R-Type 3.
 * Averted in the computer game Out Of Order. Playing the theme of The Town backwards renders it harmless, and reveals the hypnotic subliminal messages hidden within, but doesn't counteract the effect. To do that our hero has to swap out the hypno-tunes for his Three Frank Harlons album.
 * In LucasArts' Loom, many drafts can be reversed to achieve the opposite effect. For example, you can dye wool green, then un-dye it back to white.
 * In the fourth chapter of Tales of Monkey Island, Guybrush has to follow a set of steps to prepare a Voodoo recipe called the "Feast of the senses", to feed La Esponja Grande and make it grow. In the next episode he has to follow similar steps but backwards to make the Esponja shrink, as Lechuck had stolen it and was using to steal the Voodoo energies of the Crossroads.
 * In The Legend of Zelda Ocarina of Time, Link pulls the Master Sword from the Pedestal of Time and travels seven years into the future. He eventually learns that he can go back to the present by putting the Master Sword back.
 * VVVVVV has a shiny trinket that you cannot access because of an Insurmountable Waist High Fence. To get to the other side, the player has to navigate through 6 different screens filled with spiky death... twice.
 * The final game in the Bit.Trip saga, BIT.TRIP FLUX, is basically BIT.TRIP BEAT played from right-to-left instead of left-to-right.
 * Cold Hard Crash from Crash Bandicoot 2: Cortex Strikes Back takes this concept Up to Eleven to the point of almost cruelty. To get 100% completion of the game Crash must break every box in the current level he is in and collect a gem that only appears when he does so. To get all the boxes in this level you have to play through the first half without dying to activate and reach the death course, a difficult, checkpoint-free path covered in crusher traps and nitro mines, almost entirely on slippery ice. When you reach the end of the death course, you need to activate a switch and do the course BACKWARDS to get the new crate the switch spawns at the beginning of the level, at which point you take the platform back to the main level and complete it

Web Animation

 * Parodied in Homestar Runner, in Marzipan Answering Machine 9.2. Homestar mistakes "Go to Richway and pick up some Hefty bags" for "Go away and pick up sticks" for a breakup message. In an attempt to undo his response, he tries saying it backwards, but realises it doesn't work and ends up switching tapes with the machine.

Web Comics

 * Parodied in a Daisy Owl strip in which Cooper suggests that the cure for falling down the stairs is falling back up the stairs.

Western Animation

 * Courage the Cowardly Dog: Going through a tornado reduces Old Lady Muriel to 3½ years old. The solution was for Courage to put her through a tornado going the opposite direction.
 * A Powerpuff Girls episode with brain-breakingly bad physics had them going so fast that relativity started working backward and they ended up in the future. Then they somehow got back by going just as fast in the other direction.
 * It seemed more to one troper that out of sheer desperation, they actually broke the light barrier.
 * This works if the first trip was slightly under the speed of light, which thanks to relativity would move them into the future quickly with almost no time passing from their POV, and if the second trip was slightly over the speed of light, which would move them into the past quickly with almost no time passing from their POV. However, this is probably overthinking a show that works by Rule of Funny.
 * Anyone remember the end of the first Superman movie? Yeah, that's even sillier.
 * Futurama parodied this trope in the episode "Roswell That Ends Well."
 * Played literally in a Darkwing Duck episode. Darkwing Duck gets super speed, but using it makes him age extremely fast. Honker suggests he follow his course of events backwards, undoing everything he did that day, and reversing the aging process. It also removes his super speed completely.
 * Jonny Quest TOS episode "The Invisible Monster'': Dr. Quest plans to destroy the title creature by reversing the process by which it was created.
 * Space Ghost episode "Clutches of Creature King": Space Ghost is sent into the past by a "time warp caused by the cross of an energy force with a neutron ionizer". He reverses the process to return to the future.
 * Totally Spies! episode "WOOHPersize Me!": Master Mario's music has a mind control effect on people who listen to it. To remove the control you just have them listen to the music played backwards.
 * There's a similar thing in Lilo and Stitch The Series.
 * In one of his short adventures, Underdog reversed the effect of Simon Barsinister's camera ray by inserting the lens backward and aiming it at the police officers who had been turned into photographs.
 * An episode of Duck Tales has the Nephews run Scrooge's business for a day, only their products tank and bankrupt Scrooge. However, the nephews find out that children aren't allowed to run a company, so everything that happens has to be undone, which gets all of Scrooge's money back.
 * In an episode of Peter Pan and The Pirates, Michael plays a piece of music that accidentally summons a female viking who can enslave people with her singing. Michael figures out that to get rid of her, he has to play the song backwards.

Real Life
"Hammond: I don't want the record -- it's not one I want!"
 * Ultimate Example: Walk forwards. Now do the same thing in reverse. You're right where you started again, aren't you.
 * Well, no. The Earth will have moved while I was walking. Also, I might have been on a train, or a helicopter, or an escalator.
 * Real Life Example: Sandia National Laboratories has come up with a way to reverse combustion and turn carbon dioxide back into fuel. Although plants can do this (concentrate and store solar energy for later use by turning carbon dioxide and water into glucose) without much effort it's a pretty big deal for humans to be able to do it artificially.
 * This is called the Fischer-Tropsch process and has been known since the '20s. Engineering it to the point where it's efficient enough to be useful is the hard part. WWII Germany did employ it out of desperation.
 * Humans actually can also do this as well (to a degree): it's called Gluconeogenesis. It's the reverse reaction of glycolysis, the first part of the process our bodies use to oxidize glucose, and is used when our blood sugar level is low.
 * Truth in Television (sort of): All speed records have to be achieved twice to be declared official - once to set the speed, and again in the direct opposite direction - this proves that it was an official speed, and not assisted by a tailwind or the such.
 * Jokingly referred to on Top Gear, after Richard Hammond's high speed crash: Jeremy Clarkson remarks that it would have set the world record for the fastest car-accident... in the world. Only he has to do it again the other way.


 * The idea behind the alternative medicine of homeopathy might be described this way. The usual homeopathic remedy for a given symptom is to consume a substance which would normally cause the symptom, but in such extreme dilutions that the result is chemically identical to water.
 * And thus will only really cure a mild thirst.