Hold the punch if you can!
In the absence of the real tool, you can make some wooden jaws to grab the gear - drill a hole the size of the gear in a piece of wood, cut the wood in half, then grip the wood not the gear... you know the sort of thing. Gently warm the gear and worm first, either with a soft flame or dip it in boiling water. Be sure not to twist through the crank pin. A jolt will work best. Don't forget left hand thread!
Good luck.
Leon