Werkin has it. Find a comfortable cadence for the pedal stroke and inhale in some rhythmic way coordinated with the pedaling. Not too fast and not too slow. On inhaling, think of filling a water bottle from the bottom up. Take air into the belly, (think fat buddha belly) with the chest filling last. As said, on exhale, push with the belly. It will get better and you may even reach a point of standing and dancing on the pedals. I'm asthmatic so I pay a lot of attention to breathing.