Well that's not supposed to happen!! I'd really like to figure out what caused this. What graphics hardware are you using, and what driver versions? Is this on the latest build of the game?
%APPDATA% is a reference to a hidden folder in your user profile (it’s a Windows variable that expands to <your_user_profile>\AppData\Roaming, where <your_user_profile> is usually something like C:\Users\Waluigi). If you hit Windows-key+R, you’ll get a “Run” window, and if you open %APPDATA%\Godot\app_userdata\Grunk verbatim, you should go straight to the folder. You can also just paste that string to the location/URL bar in a file explorer window.
(For MacOS, you can find it here instead: ~/Library/Application Support/Godot/, and for Linux, ~/.local/share/Godot or ~/.config/Godot.)