how do i make it right or apologise

Theres this guy which i had a history with, but eventually made up, and now he started to mock me(i dont know the right word). I said to him straight up that id fight if he got up to it again. And he did, I dont know if he was pulling my nizzle(Im sure this isnt the right phrase but ill go with it) and i hit him, like i said. And i feel bad, it wasnt the right thing to do. Now hes not some close friend but i still feel really bad... I dont know hot to make it up to him, even if its hard. I feel like i warned him and he still went trough with it but then again it couldve been the bigger man and let it slide. Anyway thanks for reading