I had no idea how the Racechip app worked for the GTS (boost) and XLR (throttle pedal) before I bought them. Now that I have them I thought I could give a little info here for those who are considering the purchase. You basically have three screens.
The first is the main screen which you can select on/off, eco, sport or race mode. The fine tuning button brings you to the second and third screens. The GTS fine tuning screen allows you to select what map setting (1-7) you want to use for the race, sport and eco buttons on the main screen. The XLR fine tuning screen does the same but for throttle settings (E+, E, N, S, S+, R, R+) that you want to use when the eco, sport or race mode are selected on the main screen.