1. Type in the games name
2. Type in the version you want
3. Hit Search
Results will appear after you searched.
4. Download and install the downloaded apkAfter pressing the download button and doing what it says follow this guide to install SideQuest.
After installing Sidequest and setting it up drag and drop the file you downloaded from the download button above into SideQuest to install the apk.
Congrats. You now downgraded your game
If you need help join the Beat Saber Legacy Group Discord Server and ask for help there.