Unless you have managed to perfect the practice of time travel,
here is a tip for you:
You can't change the past.
No amount of brooding, thinking, perseverating, or fixating on it will make it different.
The past has happened, and that is that.
What you CAN do, however, is to reflect, take your lesson, and wave goodbye.
Use your energy and new found knowledge to make today the best it can be.