First buy a new spring. Then heat the bolt head with a propane torch. Make sure you have the bolt head securely clamped in a good vise. Make sure you have a good screwdriver that fits the slot well and won't slip out. Clean the slot in the screw. Lean on your screwdriver while turning out the screw, after heating it with the torch. The heat will probably kill the spring in the bolt head, that's why you'll need a new one. Good luck.