Place the firmware file on a FAT-formatted USB flash drive and plug it into the IndigoUSB while it's running. Make sure the file name stays the same.
The red LED in the device will flash several times slowly and then begin updating.
While it updates, the red LED will flash very quickly. Once it stops, remove the flash drive. Press the reset button on the device (visible through the small square opening).

INDIUSB.ROM - Updated 2018-11-02