How to find UDID on Apple TV 4K

After you have wirelessly paired your Apple TV, it will appear in Apple Configurator or Xcode's devices window as it normally does.

Thank you BTH for your reply. Obviously, I'm not the original poster, but I stumbled upon this page via a Google search. Please allow me to improve on your reply for others who may also stumble upon this page. Not everyone looking for this information understands that the "Identifier" is the same as the "UDID".

Here are complete steps to pair your Apple TV 4K to your Mac AND find your UDID via XCode:

(follow steps 1, 2 and 5 if already paired)

1. Ensure both your Apple TV 4K and Mac are connected to the same Wi-Fi network
2. Open XCode
   1. Click on the "Window" menu item
   2. Click on "Devices and Simulators"
3. Open up the Settings app on your Apple TV 4K
   1. Go to "Remotes and Devices"
   2. Go to "Remote App and Devices"
4. Your Apple TV 4K should appear in XCode's "Devices and Simulators" window under "Discovered" devices
   1. Click on your Apple TV 4K under "Discovered" devices
   2. Click the button that appears to pair your Apple TV 4K
   3. Enter the code displayed on your TV into XCode
5. XCode will pair with your Apple TV 4K and it will appear under "Connected" devices
   1. From here there is one step left: click on your Apple TV 4K under "Connected" devices
   2. The UDID will be displayed as the "Identifier"
      1. Double click the UDID (aka "Identifier") to select
      2. Control click the selected UDID
      3. Click copy in the context menu to copy your UDID to your clipboard