what youll want to do is go the the top right corner of the sidequest hud
it should have an icon called run abd commands,
adb install C:\Users\YOURUSER\Downloads\beat-saber.apk
paste a command like this into there and it will install automatically, just change youruser to your user name on the mac, change the location if its somewhere else, and the name to togethervrm.apk.
Hope this helps