Is there a way to 그랜드토토 the software to default settings and preferences?

Close the program. Now press CTRL+SHIFT while double-clicking on the program's icon to launch it. You should see a window that asks "Do you want to reset all preferences to default values?" Click Yes.
On a system running macOS, this may not work if you are trying to launch the application from the Dock. If you do not see the 그랜드토토 dialog, try repeating the process with the icon found in your Applications directory in Finder instead.