>That theory would prove that you could go back in time between universes.

Well, no, because then you'd have to know how to find that other universe.. and if you could find that, then you could find any split of the infinite number of universes and pick the one that suits you most, but then there would already exist a universe where that happened and likely you are already in it.

And if you can find these universes, what is stopping you from finding the infinite number of universes that hold that future by all possible decisions that can be made?