It's the same as with belly fat/six pack: man boobs (in 95% of the cases) come from a high body fat percentage. Your genetics just defined that fat is stored there mainly. To lose it you need to reduce your body fat level overall, there's nothing you can do to make your body lose it in a certain area. Exercises will just tighten everything and may even make the boobs look bigger!
So my advice is: eat clean and work hard (on your fat depots)! Good luck!