Ensure RC inputs move in the right direction as documented at Radio Control Calibration — Plane documentation In particular the green bar for pitch should move in the opposite direction as the physical stick on the transmitter. If anything moves in the wrong direction reverse it on the transmitter.
As documented at Four Channel Planes — Plane documentation, with the model in FBWA, tilt the model and ensure that everything moves correctly on the model to bring it back level(using SERVOn_REVERSED to reverse output channels as needed).
Switch to MANUAL mode and ensure that moving the transmitter sticks move the control surfaces as expected. If this doesn’t work a previous step was not done correctly.