A few tips to add to the previous helpful posts:
1) Use a flat thin (~1” x 5”) flexible plastic strip (cut from a plastic disposable food container) to jimmy the microwave door open.
2) Use a thin screwdriver or stiff metal wire (e.g., from a wire clothes hanger) to pop the trim screw covers (if you have them) from the other side so as to not scratch the pop-on covers.
3) Keep the microwave level when moving it, so the broken cam piece doesn't get lost under the microwave.
4) Use a Torx security T15 bit to open the case.
5) Use a minimum 1 inch #4-40 screw and nut. It will be easier if the screw is 1.25" or 1.5".
6) Put a tooth/serrated washer before the nut to prevent loosening. I did it the first time without the washer and the screw loosened, the post got wobbly, and the plastic lever popped out after 8 months. So I put a tooth washer in the second time.