Hey! There's no exact way of getting your boyfriend back.
It really depends on why you broke up. If you broke up out of a huge fight, then maybe not so much. But if it was just a "this isn't working out" thing, then you may have a chance.
Wait and see. Talk to him, chat him up in the hallway. Just become his friend again, then ask him out. If he says no, say friends. Don't let a breakup come between you.
Good luck!
All the best,
Nora