We need to retrain ourselves to breath correctly, many excersises have been developed around this subject so I am certain you will find one that suits you.
But the simple one I use is
Gently interlock your fingers, place your hands on your belly.
Breathe in filling your stomach with air, as you do your hands will fall apart.
Breathe out relaxing your stomach and your figers should interlock again.
Count your breath in and out (keep them the same length and increase the duration as you improve)