https://wccftech.com/apple-seeds-beta-4-of-tvos-12-and-watchos-5-to-registered-developers/

Apple has seen fit to release the beta 4 of watchOS 5 and tvOS 12 to registered developers. The updates arrive two weeks after the company rolled out the third beta and more than a month after it was initially announced at the WWDC 2018. tvOS 12 and watchOS 5 have a lot of new additions in store for users. If you’re a developer and want to check out what’s new in the latest beta 4 then be sure to download it on your respective device. Let’s see some more details on what the new beta version has in store for developers.

If you happen to have the fourth and or fifth generation of Apple TV, you can download the tvOS 12 beta 4 from the Apple Developer Center. Be sure to note that a proper profile is required to install it through Xcode on Mac. Subsequent beta versions can be downloaded on the Apple TV through the Software Update mechanism.