For the desktop version, download the MusketGameHE_0.1.zip file. Extract it, connect your VR goggles to your PC, and then run the .exe file in the extracted folder.
Alternatively, turn on your compatible standalone VR goggles (Quest 2 or better), and then – while in the goggles’ internet browser – download the MusketGameAPK_0.1.apk file. You’ll have to install the file, which is more complicated than it should be. Just look up tutorials on “How to install APK files on Quest 3” or smth like that.