Some games are just the one size, you may be able to
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to change but the game won't. There's one game that's only 900x1000, if your monitor is under that there doesn't seem to be a way to make it fit.
Check the games options menu if you can get to it for any resolution setting, occasionally they'll be in a separate exe called something like config. If you think the game should fit but doesn't, you could try right clicking the games exe and turning of any screen scaling in the properties.