The tvOS 12.3 public beta can be obtained by going to the Settings app on the Apple TV and navigating to the Software Updates section under "System." "Get Public Beta Updates" will need to be toggled on, and once it is, the Apple TV will download the beta software.
tvOS 12.3 includes the revamped Apple TV app that Apple debuted at its services-focused event on Monday. The new TV app is a better version of the original TV app, offering up access to TV shows, sports, news, and more in one spot.
There's still a "Watch Now" section with an "Up Next" feature for keeping track of what you're in the middle of watching, but there's a new "For You" feature that recommends new content based on what you've previously watched.
A new "Channels" option lets you subscribe to third-party services like Showtime, Starz, and HBO right within the TV app, and you can even watch all of the content from the services included in Channels right in the TV app without having to open a third-party app.
Channels will include CBS All Access, Starz, Showtime, HBO, Nickelodeon, Mubi, The History Channel Vault, and Comedy Central Now, but during the beta, only Showtime, Starz, Smithsonian, and Tastemade are accessible. You can subscribe in the TV app and get a one-week free trial before you're charged.
The TV app is on the Apple TV and iOS devices, and it's even available on the third-generation Apple TV through an upcoming software update that Apple plans to release.
Apple has said the new TV app is coming in May, so we can expect tvOS 12.3 to be released then.