Please contact help@3drobotics.com to get the firmware file. The proceed with the following steps to load it:
Using mission planner:

  1. Go to config/tuning, planner, and select advanced view.
  2. Go to initial setup, install firmware.
  3. Click Load custom firmware and select the firmware file.

Using apm planner:

  1. Click file, and select advanced mode.
  2. Go to initial setup, install firmware.
  3. Click custom and select the firmware file.