Garmin G3X Pilot's Manual page 139

Adjusting the Fuel Remaining or Fuel Used quantity:
1) Move the FMS Joystick to the Fuel Remaining or Fuel Used Field (if
necessary).
2) Turn the FMS Joystick to adjust the desired quantity.
Resetting the Fuel Used to zero and Fuel Remaining to full tanks:
Press the RESET Softkey; this resets Fuel Used to zero and Fuel Remaining
to the maximum fuel capacity for the aircraft
Resetting Fuel Remaining only:
Press Softkey #2 (XX GAL); this resets only Fuel Remaining to the
maximum fuel capacity for the aircraft. XX is the airframe specific full fuel
quantity.
Resetting Fuel Remaining to partial fuel quantities (optional):
Press Softkey #3 or #4 (XX GAL); this resets fuel remaining to a partial
tank quantity (i.e., filler neck tab). XX is the airframe specific partial fuel
quantity (if configured).
190-01115-00 Rev. K
'Confirm Fuel Quantity' Reminder Page
Garmin G3X Pilot's Guide
EIS
117