The FPV monitor I have for my drone also has a HDMI input and I have been able to connect it to the Windows 10 laptop I run FPV Freerider on as a secondary display.  It would be really cool if I was able to run FPV Freerider using my Taranis as the controller and using my FPV monitor for output, but the program starts up fullscreen on the primary display and appears to have no option to move it.

I you press Alt+Enter on Windows, it changes to windowed mode. 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 wish you can also adjust the resolution to fit your goggles.  

You change the resolution by adding command line parameters to the exe file as described in the manual. For example:
-screen-fullscreen 0 -screen-width 800 -screen-height 400

(That will run the simulator in a 800x400 window)

To be able to select different displays you might also be able to use the -adapter command line argument. Have a look at the Unity Standalone Player command line arguments here:
https://docs.unity3d.com/Manual/CommandLineArguments.html

(Under "Unity Standalone Player command line arguments")

Great, thanks.  I look forward to trying it.

Or you can simply mirror the two screens. That's what I do with my Skyzone goggles. They have an HDMI input and what I see on the googles is exactly what you see on the computer. Full screen works perfectly.