You need to remove the two screws that hold the battery holder in place and remove the battery holder. Then remove the three piece power switch panel as well.
Then you need to remove the "C" clip that holds the guts inside the shell. Small needle nose pliers can sometimes get the clip out.
Then all the guts should come out of the microphone. There is an additional part or two to remove and the piece that fits around the on off switch was missing.
Here is a picture of the new on off switch. I soldered it using the head mounted magnification lenses.