Use the ProPresenter “Screens” menu to open the ProPresenter Screen Configuration:

Verify that you see the following display connections:
If you need to verify the current Mac Displays attached and their arrangement:

Open the settings (grey gear icon), and select Displays.

All displays should be at a resolution of 1920 x 1080.

Use the “Arrange” button (bottom right) and verify each displays position by hovering the mouse over each one.