Mistakes that we’ve already made in the past can’t be unmade. You can learn from them, and try to avoid making the same mistake twice, and try to make amends for them, but you can’t get an actual do-over. People often beat themselves up for mistakes made in the past, which is silly. People may think that if they feel bad, that cancels out the mistake somehow. But it doesn’t. It also wastes time that could be better spent learning and being productive.
People often make a bunch of mistakes and then feel overwhelmed. One thing that may help with that is to think about the fact that there’s always a Right Thing† to do regardless of your situation. Then, rather than feeling overwhelmed by the burden of many years of mistakes, you can just try to do that Right Thing.
If you Quantum Leap’ed into somebody else’s body somehow, there would be a Right Thing to do - an appropriate way to act. This applies even if the person is terrible. In the case of a terrible person, the Right Thing might be to turn yourself in for committing a horrible crime. So just do that. And most people aren’t people who commit horrible crimes and won’t have to spend a bunch of time in prison. So doing the Right Thing shouldn’t be too bad for them, relatively speaking.
Imagining quantum leaping into somebody’s body is fanciful, but I think it helps make things more objective. Rather than start with your own situation directly, it might be easier to imagine doing the Right Thing if you were (very literally) in somebody else’s place - even a really bad person. Then you can turn it right around, and imagine what a person trying to act decently would do if they were in your place, and just do that. Hopefully with this thought exercise, you can get some perspective on how your situation isn’t actually so bad, and also think more objectively about what you should do.
† There might be a range of Right Things that differ in details. It’s hard to figure out the Perfect, Optimal Thing, but I mean more like, there’s some basic approach that you can take that is the right thing to do