If your game window is too large, I figured out how to navigate (with the default keyboard layout) so I am here to help
After starting the game, you'll see the standard disclaimer (depictions are fictional, not real, etc) and the seizure warnings.
After those, press space bar. Wait a moment then press space bar again
After the second space bar, you will be at the main menu. Press down arrow twice and enter key
Then you will be in the settings menu. Press the 3 key a total of 4 times to naviate to the video tab
Press the down arrow 5 times to get to "windowed mode"
On this setting, you probably want the middle option. If a different one is selected, press A to navigate left or D to navigate right in order to select Windowed Borderless.
Press the down arrow again to go to resolution
This one will depend on your monitor. Check your Windows resolution settings to see what Windows uses, and make the game match that.
After this, press the down arrow twice and the right arrow once, then press enter to Apply the settings.
This should immediately bring the window back to a functional size.