I you press alt+enter on Windows, it changes to windowed mode (same as adding command line "-screen-fullscreen 0" ). Once in windowed mode, you can drag it onto the correct monitor, and then press alt+enter again to go back to fullscreen mode.
If you are having trouble with resolution the best solution is to create a shortcut of the FPVFreerider .exe file.
On that shortcut, you can add command line parameters to set the resolution.
For example:
-screen-fullscreen 0 -screen-width 1920 -screen-height 1080
(That will force the simulator to run at full HD 1920x1080 pixels windowed)