To watch the stream on your Apple TV you have to start the stream from your iPhone, iPad or Apple computer.
Stream from iPhone or iPad:
Use Screen Mirroring to see the entire screen of your iOS device on your Apple TV or AirPlay 2-compatible smart TV.
Connect your iOS device to the same Wi-Fi network as your Apple TV or AirPlay 2-compatible smart TV.
Open Control Center:
- On iPhone X or later or iPad with iOS 12 or later: Swipe down from the upper-right corner of the screen.
- On iPhone 8 or earlier or iOS 11 or earlier: Swipe up from the bottom edge of any screen.
Tap Screen Mirroring.
Select your Apple TV or AirPlay 2-compatible smart TV from the list. Need help?
If an AirPlay passcode appears on your TV screen, enter the passcode on your iOS device.
Your TV uses your iOS device's screen orientation and aspect ratio. To fill your TV screen with the mirrored iOS device screen, change your TV's aspect ratio or zoom settings.
To stop mirroring your iOS device, open Control Center, tap Screen Mirroring, then tap Stop Mirroring. Or press the Menu button on your Apple TV Remote.
Stream from your Apple computer:
Make sure your device is on the same WiFi network as your Apple TV.
Mirror your screen by clicking the icon above which should be visible at the top right of your screen.
The following Apple computers support screen mirroring to Apple TV:
iMac (mid 2011 and later)
Mac Mini (mid 2011 and later)
Macbook Air (mid 2011 and later)
Macbook Pro (mid 2011 and later)
Mac pro (mid 2013 and later)