Unplug the microwave from the wall outlet. The microwave power cable is typically plugged into an outlet located in the cabinet above the microwave.
Open the microwave door.
Pry the inner plastic panel of the microwave door off, using a flat-head screwdriver. Be careful when prying so that you do not crack or break the plastic panel.
Tighten the screws securing the door handle to the door if the handle is loose, using a flat-head or Phillips screwdriver.
Remove the screws if the handle is broken or in need of replacement.
Align the new handle up with the screw holes, then secure the handle using the screws removed from the original handle.
Align the plastic cover on the inside of the microwave, then snap it back into place.
Restore power to the microwave.