Contact the manufacturer. They should be able to provide you with a replacement. You will most likely have to replace the bolt as well. Or you can use a tap, it's easy but you will probably have to repair the bolt as well. You can use the good bolt to determine the correct size. If you opt to take apart the microwave you will probably need a t15 torx security screwdriver as well. Most microwaves use them for some of the screws. Be wary of electric because some capacitors will hold a charge even without power.