Specifically, what exercises to do to work them off.
In general, it is not possible to have spot weight loss. The areas you store fat are personal and genetic and the fat is all distributed across your body and even surrounding your important internal organs. It all comes off at once as you get closer to your goal weight.
Women have the same thing in reverse, they may be overweight with an ample bosom and want to keep just that pleasant bosom, but it’s not possible.
Keep on lowering your weight and you’ll see more muscles and less man boobs.
One dietary thing: soy is estrogenic in guys and it has been known to enlarge man boobs if you eat mass quantities. Like soy protein shakes etc. Does not appear to work that way for the ladies.
Medication thing: some meds have man-boob side effect.
Aging thing: reduced testosterone production as you age, can encourage man-boobs.
Bottom line: they’re fat. Lose weight.