How do you train your quaker parrot from biting?

The key is to not be afraid. If your bird bites, don't yell, hit it, jerk back, cry/laugh etc. That might cause the bird to bite again in the future just to see your reaction. Hold still or give it a gentle push when it bites to show you won't stand for it.

If you haven't already, you'll want to teach it the 'step up' and 'step down' commands (google it, there's lots of sites with instructions).