If you subscribed to Smithsonian Channel Plus via Apple TV Channels, it's easy to subscribe to Paramount+. You can try it free for 7 days, and after that, it's only $9.99/month. Please note that you'll be billed via iTunes.
  1. Open the Apple TV app.
  2. Search for the Paramount+ channel (you may need to scroll down your screen, where it's listed under "Channels").
  3. Tap the "Paramount+ Free" button.
  4. Confirm iTunes billing information.
That’s it! You now have access to the Paramount+ channel on Apple TV Channels.