The project page is located on the GitHub site. There you have all the information to build the patcher binaries(not the patched YouTube apk). Then patch the YouTube apk (must be official original apk) from the command line (instructions are there on how to do this).
Building the binaries on your own can be overwhelming for many so the easiest way is to download the “ReVanced Manager” (needs Android 8 and above).
Unlike Vanced Manager, ReVanced Manager will not download any apk and microg (for non-root devices). It will show you the installed official YouTube version on which to apply the patch. It also allow you to specify an offline YouTube apk stored on your device which you want to patch. It will then display the list of available patches. You can choose the patches as per your requirement and apply them. Once the patches are applied successfully, you will see an option to install the patched apk as a non-root user or “install as root”. If you are applying patches on the installed YouTube app, then depending on the patches you choose you may get the warning saying something like “split configuration detected. The patches you choose requires resource patching, hence you may encounter some errors”.
I was not sure what to do so I choose to apply patches on the offline apk.
Important: The ReVanced Manager doesn’t seems to recognise .apks or .xapk extensions so your offline apk needs to be a single apk (you can get the apk from trusted site like apkpure or find a way to extract the split apk’s from the installed app and merge them into a single apk).
One more thing the patched apk will not install over your existing installed official apk. So you must remove it first. I am also not sure if the patched apk will install over a previously patched apk created with the ReVanced Manager (It should be possible but I came across this project just last night and haven’t really tested the various scenarios).
