1. Join a random game. In my case, I mostly join British Sergeants Mess Annex & Invade (filter for "British").
2. Press ESC, click on Configuration, and then Controls.
3. Change some control settings, for example: helicopter movement --> move forward set to mouse UP, and move backward set to mouse DOWN (by the way: the other way around is ridiculous guys, please change this by default).
4. Click OK, click OK again, and close the menu.
5. Everything seems fine, the changes have worked.
6. Press ESC again, click on Configuration again, and then Controls again.
7. Boom, everything has been reverted to before you made the initial changes.