http://wccftech.com/downgrade-tvos-11-gm/

Here’s how you can downgrade tvOS 11 GM back to tvOS 10 on Apple TV in a few easy steps.

Whether you are a developer or a public beta tester, the tvOS 11 GM is now available to you over the air as a free download. Developers, on the other hand, have the luxury of installing the firmware from scratch, since they have access to the restore files straight from Apple itself. But, if for some reason, you believe that you have made a mistake updating to tvOS 11 GM, then you have the complete option of rolling back to tvOS 10, as long as Apple is signing the aforementioned firmware from its end. All you need is a USB-C cable, an installation of iTunes on your PC or Mac and a little bit of patience.