From my understanding, there is no registration. Apparently the Samsung Members app will auto detect your device and show you a banner with the option to join the beta. However, I am yet to get the banner to show on the app for my 20 Ultra.
Just saw that Samsung will be releasing the beta to Note 20 users Monday October 26th. From my understanding you need to have an unlocked Note 20 in order to join to beta program. This is exciting news, can't wait for the 26th.
Also I keep reading about an October patch that will help improve the camera. However, I still haven't seen anything on my own Note 20 Ultra device.