ProFlight Challenger User Manual page 8

If the aircraft drifts in a particular direction you can trim the controls using the
trim buttons. Select the trim key opposite the direction of drift.
Should you need to reset the drone after an impact for example, set the
aircraft on a level surface and with the transmitter and aircraft turned on and
connected, move both control sticks to the bottom left and hold for 10
seconds. The lights on the aircraft will flash until the reset is complete. This
will return the trim settings back to default.
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