It is most prob a horse shoe clip that holds it on. Take a large flat blade srewdriver and put it between the rear of the winder handle and the door trim and pull the srewdriver outwards so a gap appears between the trim and handle. Have a look into the gap and you should see a piece of wire. Take a small srewdriver and push on the open end. THEY ARE SPRING CLIPS SO KEEP AN EYE ON IT CAUSE IT WILL COME OFF UNDER TENSION AND MAY WELL FLY QUITE A WAY. Put the clip onto the handle when you refit it, then put it on the splined shaft and give it a good fairly hard hit with the heel of your hand to refit it. Failing all that see if there is a plastic ring on the trim side of the handle. If there is try pushing that in the opposite direction to where the handle arm is pointing.
Simon Mayes, October 2005