I have a dual monitor setup, needed clarification. I will test and see.
Edit:
Killom I see your problem. Windows 10 lists my left monitor as #2 and my right as #1, however, my radeon settings lists my #1 monitor as the left and my #2 as the right. I believe my radeon settings determines which is my primary monitor for fullscreen things, and I can't seem to be able to send it to my other monitor without making my other monitor my primary. If you're not averse to changing which of your monitors is your main screen, you can do it that way.
I tried starting my game in windowed(which is how I use Starmade) and dragging it over, using alt+enter to switch to fullscreen, but Starmade does not recognize the shortcut key.
A third option is a program called Display Fusion
or something similar. It has a function for sending an application from one monitor to the other whether it's fullscreen or windowed. I'm not currently running that, but I do know it has that function.
Edit2: I have checked, you need the paid version of that particular program to use that function, here is link if interested:
DisplayFusion
Alternatives:
DisplayFusion Alternatives and Similar Software - AlternativeTo.net