I used a USB C male to USB A male or USB C male cable (I think it needs to be USB 3.1 spec too), to attach the ATV to a Mac. Then you use iTunes to restore back to 11.2.5. I had to download the .ipsw file from the internet though, as the Apple TV recovery server was constantly reported as unreachable by iTunes.
Ah so you can only do it with the ATV then not the 4K?