Your first step for tilted horizon issues is a IMU calibration, followed by a Gimbal auto calibration, both in the DJI Go app. These calibrations should be good for whatever app you're using when recording video.
After that, if you still need to, you can do a gimbal roll adjustment in the DJI Go app. Ask if can't find the location in the menus to do this from.
And you can make that same gimbal roll adjustment while flying by doing a PRESS+HOLD of the C2 button while turning the Exposure Compensation dial (the one on the right) and view your adjustments on your FPV screen, also while using the DJI Go app.
However, I still have not yet determined of those gimbal roll adjustments are still applicable outside of the DJI Go app, such as when you switch to the Litchi app. As far as I can tell, the adjustments do not apply to video shot with while using Litchi.
DJI has so far been mum on this on their own forums.
Does anyone here know if DJI Go Gimbal Roll adjustments should still be reflected while using Litchi? If not, is there a gimbal roll adjustment in the Litchi app that I have yet to find?
Thanks, Chris