So for non-steam installs, you can manually edit preferences by going to the main X-Plane folder > Output folder > Preferences folder. TO restore all defaults, rename, move or delete the entire preferences folder. Or you can try to find which specific preference is causing problems and edit it in a text editor.
Again, I'm not sure what the file path for Steam installs are, or if this is even a good idea. You could ask on the Aerosoft support forum, or possibly in Steam community support.