How about change the way you behave for the future? That's more convincing than apologising for the past.
Some friendships stay broken and that's the risk you take when you behave badly to someone. There is no automatic right for everything to be made OK again. The trick is to learn from it. Try to build something good out of a bad situation. Try not to make the same mistake again.
You can't change the past but you can change the future.
Kris