There is one way to change the past and it is the only meaningful way to do it.
It is to change the way we think about the past, thus altering how the past affects our present and future.
It is to reinterpret the past and come up with a better story. It is to figure out what you learned from those past incidents that continue to haunt you. It is to see each mistake, failure, disappointment, break up, betrayal, as a chapter, not the end.
When it comes to relationships, what I’ve read is this: in your memory, go back to the times you were still together. Remember the joy and love you shared with each other. Go back to that place, enjoy, feel all the warmth, and stay there. This alters the frequency between you and eventually, the conflict and hurt melt away, and you might be back in a relationship with them again.