As you work on removing the trim piece over the galley and electrical panel, be careful that you do not snag or damage the vinyl covering on the top back edge of the galley. You might try a piece of cardboard or something similar to protect to protect the trim piece at that point. The microwave is held in place with 2 bolts that have the rubber pads. I believe they take a 1/2" wrench or socket. They just clamp the microwave down against the shelf it sits on. While you are there, you might decide whether you want to plug anything else into the empty receptacle of the 110 volt outlet for the microwave.
With use the microwave may have a tendency to move a little with use.