i accidentally forgot to lock my xp to 79 since i wanted to twink and reached 80

How can i turn back to 79lvl i am really burned becouse of this and anoyed and dont feel like playing help please.

start a new character and pay more attention next time.

Take several deep breaths, remember that it is just a game. Go take a walk.
Or just search Trade section and buy character of lvl 79.