Window is invisible: need help resetting the resolution preference

In-game I set my resolution to 800 x 600 by accident. My screen is 1920 x 1080. But anyways, when I launch the game, it changes my resolution on my whole monitor to 800 x 600, which I think is normal. The issue is that when I click on the game, the window is -1 x -1, meaning I can't use it since the window is invisible, and only 1 pixel wide, and 1 pixel tall. I would appreciate if someone could help me reset my resolution 'preference' back to normal.😞