Are you trying to figure out how you can get your ex girlfriend to come back to you? You had been a jerk to her and she said enough and left you. What was it you did exactly? Did you treat her poorly or cheat on her? There are many things it could have been but the bottom line is she is gone. Now how do you get her back?
This is not going to be an easy task, but if you really want to get her back be prepared for a lot of mental work. If you are lucky she may already be thinking of getting back with you, that would make your job easier but you would still have to face the issue of being a jerk to her.
However if you decide to take on the task of getting your ex back yourself, first take some time to get your thoughts in order and let her do the same, about 3 to 4 weeks would be good. Do not call or email her so you do not look needy or try to talk her into coming back to you. This will again make you look like a jerk and push her away.
Do not try to hang out at places you know she hangs out, nor bother her friends to find out what she is up to. You want to look like you are doing just fine on your own. What you can do is prepare yourself for the time you do start to try and get her back. Fix whatever it was that made you a jerk to her. She is not going to want to deal with it again so now is the time to change.
When you get your first chance to talk to her, suck it up and apologize for how you treated her and mean it. Now you must never go back to that way of treating her again or you will have blown it for good.