Your past is your imagination.
You put in what you want and get rid of what you don’t want. You create that past to make your present reasonable, to justify your present. You don’t like your past only because you don’t like your present. You are using your non-existent past as an excuse. You imagine your life would be better if something hadn’t happened to you or you’d done something. You are living in the possibilities, but it’s no more than possibilities.
You can’t change your past. And if you keep dwelling in that and don’t do something now, you’ll change nothing.