I play a Hohner melodeon (D/G) and an English concertina...same family of instrument. I bend notes by starting a normal push or pull on the bellows and then put a little more muscle to it. The result is a louder sound but the tone bends. If I shake the bellows on the push or pull I get a vibrato. The trick is to not overdo it. Remember, less is more.

Have a good time. You might want to give Planet Squeezebox a listen for the incredible variety of music played on free-reed instruments.