Issue that makes the game unplayable :(

got my friend to get Don't Starve Together, he was messing with his settings and set his resolution super high to above 3060, his monitor isn't that size and only a quarter of the game was showing on his display being the top left. Because of this he can't reset it to the normal resolution even when he goes in the game files or tries to use the arrows keys, or reinstall and he also doesn't want to factory reset even though it is a possibility. Any tips on how to fix this problem?