%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.)