I updated the firmware on my Matrice 100 RC controller using DJI Go app on my Android phone. Now the led light on the RC controller is cyan(light blue). How do I do a factory reset on the controller, or fix the failed firmware update somehow?

Please try this:
Press C1+C2+video record button+ right upper wheel, turn on the aircraft and try to update the FW again.

DJI-Tim,

Thank you for the reply. I was able to reset the controller and successfully update the firmware.

For completeness to reset the controller and update the firmware:

Plug a smartphone that has the DJI Go app into the controller
Press and hold C1+C2+video record button+ right upper wheel.
While still holding the buttons turn on the rc controller.
Let go of the buttons.
Launch the DJI Go appSkip the advertisments
Press the camera button
Press the Red warning "No Signal" (this is actually a button)
Press Overall Status
Download Firmware update
Install Firmware update