I have done the same thing. Use a small punch or jeweler's screwdriver through the slot in the hammer to push the torsion spring (which should still be installed inside of the trigger body) out of the way while reinstalling the hand in the trigger. You'll know when you've got it, the torsion spring will put pressure on the hand to rotate forward. When reinstalling the trigger into the frame, you need to gently rotate the hand counter clockwise a few degrees against the spring pressure and then guide it into place in the slot in the breech face.