4 digit code Apple TV
How can I find out what this is as I have forgotten
The 4 Digit code is generated automatically by the Apple TV, there’s nothing for you to remember, because you don’t set it, and it is different every time. It should appear on screen of the TV connected to the Apple TV for you to type into a device trying to airplay to it.
You can go into the Apple Tv settings to disable this option, or change it to use a password of your own creation.
See here: link-> AirPlay security in Apple devices - Apple Support