In Aerofly FS 2 you can repeat each flight school lesson as many times as you want. But the ratings can´t be reset individually. However, if you want to pass all the lessons again there are two possibilities for a complete reset:

1. Delete the Aerofly FS 2 via the Steam Client and restore.
2. Go to the user directory C:\\User …\MyDocuments\Aerofly FS 2 and delete the file “mission_progress.tmp”.

The advantage of the second way is the joystick settings will not be reset.