How do I adjust Start/Taxi Fuel and Reserve Fuel with Performance?

Start/Taxi Fuel and Reserve Fuel are not calculated for each flight but instead are based on the default values set for each aircraft. You can change these values from the Aircraft Edit Page by going to MORE > AIRCRAFT and selecting the aircraft you want to edit, then scroll down to the Fuel section to adjust the values.

If you only want to adjust Start/Taxi Fuel and Reserve Fuel for a single flight without changing the default values for other flights, you can do so while viewing a flight plan in the Flights view by scrolling down to the Fuel section of the planning form and tapping on the blue numbers next to Start/Taxi Fuel and Reserve Fuel.  This capability is only available with the Performance Plus plan.