Hell Let Loose: Changed my resolution, now I can't click

You can start by launching the game and press Alt+Enter to go into Windowed mode where you can then change the settings again. Alternatively, you can reset your entire game settings by following these steps:

1. Click on the Windows logo, type %localappdata% and Enter
2. Open HLL folder and go to Saved > Config > WindowsNoEditor
3. Delete the GameUserSettings.ini file
4. Launch game and retest saving your settings