How do I stream cbs all access on my Apple TV?

If you have an Apple TV HD or 4K then you would download the app from the app store, or subscribe directly in the TV app. If you have a 3rd gen then it has preset icons for server-based channels so if you can only access it if it was available on your main menu, or subscribe via the TV app. However, CBS All Access will be rebranding as Paramount Plus on March 4th and they have issued a statement that the 3rd gen will no longer be supported as of that date. Users will still be able to use airplay to stream from iPhone/iPad though.