If you had one chance to do something differently, what would you do?
The reality is, we can never change what is, what has happened has happened.
What we can do is accept that, so as to allow ourselves to be free from blame, guilt, judgement, pain, suffering and so on. When we are free and acting from our very essence, consciously in this moment, then we can do anything differently.
However, it has to be now, otherwise as soon as it becomes something you are going to do, as in the future, then it no longer flows from our soul, it is a thought projection of something that does not exist.
Act now always from the heart and soul, it is likely then that there will be very little that you will need to ever do differently.