To send a fuel request from ForeFlight Mobile, go to the FLIGHTS tab and select the flight you would like to order fuel for. Select FUEL ORDER and fill in the fields provided. Ensure the fuel quantity is correct and be sure to specify if you would like your aircraft fueled upon arrival or immediately prior to departure. You can enter any additional comments you would like to communicate to the FBO in the Comments/Requests field. For more Information see the video below.
Video 1. How to send FBO fuel orders from ForeFlight Mobile.