Reset Button

We can easily fix blowing the whole Earth up by simply pressing our friendly neighborhood Reset Button!

An event or series of events that undoes any recent events the main characters experienced so that said events never really occurred or appear to have never occurred, making them Non-Canon in some cases. You got all that? Episodic TV shows are partially immune to past happenings being considered Non-Canon as every following episode acts like a Reset Button (unless there is a Two Parter). However, it isn't always necessary to press Reset Button at the end of these shows if the new information gained from it is canonical and (planned to be) revisited later in the franchise. Reset Button can be totally avoided by having an Experience Souvenir make an appearance, alluding to the past events and showing that they were, in fact, real.

Reset Button is surely a powerful and helpful tool of an UnTrash, but the extent of its power is dependent on the events that precede its playing. The more non-canonical or outlandish the story is, the less sense Reset Button would make when it's hit. For example, it's easy to play Reset Button to end a story where a character gets a pet (by having the pet run away, have it revealed that the pet belonged to someone else, make the character who gets the pet unable to keep it...), but concluding a story where, say, a character annihilates their hometown in a Nuclear Explosion would almost certainly require a Dafuq Solution or playing, God forbid, All Just A Dream to solve the problem.

There are some UnTrashes that can be considered Reset Buttons. All Just A Dream is a terribly infamous example of such an UnTrash. In it, the dreamer is shown going through a realistic series of events that might lead to a fatal end. However, just before they die, they wake up and notice that their experiences weren't real, resetting to the time before they fell asleep. Another form of a Reset Button is a Factory Reset where, at the end of the story, characters (likely main ones) forget certain details of recent occurrences.