To change the Fuel quantity in the MFD, follow these steps:
1) power on the avionics
2) go into flight mode (accept the confirm messages)
3) using the knobs on the bottom of the unit, switch to the Aux tab
4) on the left side of the MFD you have 5 illuminated buttons; hold the top and third (L1 and L3) for approximately 20 seconds, the screen will flash and you will be in Maintenance Mode. (if you are not on the Aux tab, holding L1 and L3 will not work)
5) select Engines (either right or left side of the MFD - illuminated button)
6) Fix the Fuel Qty; based on the aircraft manufacturer specs
7) Save
8) return to MFD