Hi!
I'm someone who frequently has issues with resolution and screen problems. Damn you cheap PC!
Alt+Enter may be an option, but you can access the settings for this by opening the 'Mir2Test' file in your mir folder for Valkyrie. Simply change FullScreen= to True instead of False.
And if like me, you have the issue where your mouse pointer is 'off' you need to change the resolution to your display settings to fix it
