A time machine? Look, time travel, the kinda of time travel that you're thinking of, is a scientific impossibility.
It would violate the second law of thermodynamics.
You're talking about regrets, so if you want to ask about regrets, just ask about regrets, and leave all this time-travelling no sense out of it.

- Walter White to Saul Goodman in Better Call Saul S06E13 "Saul Gone"