Is it running on a Teensy, Pro Micro, or something else? In any case, this is from the Soarer's docs:
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The Teensy family have the PJRC bootloader installed and are programmed using PJRC's Teensy Loader, available for all common OS.
Other breakout boards usually have the Atmel DFU bootloader installed and can be programmed using FLIP.
FLIP is available for Windows and Linux. For Mac OS-X, see <Link no longer valid>.