Some people have used heat guns with good results. I have used the Hot tap water to shape them and imediately submersed them in ice cold water to hold the shape.
I had one that didn't want to keep it's shape and ended up doing the hot/cold water thing again with the part secured to a small coffee can with rubber bands for a week.
Bend slowly and carefully. Fiberglass can be quite flexible but the gel coat usually isn't quite as forgiving. Stress cracks can result from over flexing.