Changed the game setting for resolution to be 1980 x 1080 fullscreen but now the game only show the top left of the screen of the main menu which makes it to where I can't even access the setting ingame since it's now offscreen.

I've tried uninstalling the game & deleting all the files but when I reinstall it the setting are somehow saved form previous change even though I told it to uninstall everthing including my saves.

You might be able to fix the problem: right click on the game's icon in Windows explorer, select the compatibility tab, and check the "Disable display scaling on high DPI settings". Depending on the version of your OS, the wording might be different.

To answer your actual question though, you want to delete the file C:\Users\YOUR USER NAME\AppData\Local\Zombasite\User\user.cfg to reset all of your settings. I believe AppData is hidden by default.

It was your suggestion for the DPI settings that helped me resolve this. Thank you for the help.