The instructions are on itch.io but I will tell you if you don't want to go back and forth.
IF ITS NOT ON APPLAB YET
1. Download and open Sidequest and connect your headset using a USB or oculus charger
2.If it asks anything about allowing or not allowing, click ALLOW
3.Make sure you have developer mode and an oculus/meta organization to use connect your headset to Sidequest (Has set up instructions if having issues)
4.Download the game through itch.io
5.On Sidequest, find the Install APK option at the top right corner and select the game/APK from your files
6.Wait for it to download and play
7. Done
IF ITS ON APPLAB
1.Go on your VR headset
2.Go to the store
3. Search and look up the game
4. Download it and wait
5. Play the game
6. Done