You go build a time machine and go back in time, give the plans to a past version of yourself and build it with him, later on, the two of you decide to use the machine to go back to the same moment and give the plans to a second past version of yourselves. Since this would result in a paradox if there was only one timeline, there must be multiple timelines, meaning that the possibility of functional time travel must imply that multiple timelines exist. A paradox doesn't destroy the universe, its not something that risks the integrity of reality if it does occur, a paradox is an impossibility, something that by definition cannot occur because it refutes its own possibility. The woman in this sketch is a midwit.