How do i replace Cannon cd2 door magnet?

The door magnet has snapped off from the screw thread, which is still in the oven casing. It is a Cannon cd2 oven I can turn the small amount of screw thread still protruding but it does not move in or out as I do. I was worried what ever is holding it on the other side might drop off if I succeded. I am reasonably adept at small engineering projects but want to know what I'm leading myself into. How do I replace the magnet with one I know I can buy on the Internet?
Any advice gratefully received.