Restore Apple TV 3rd generation to factory settings

You will find the instructions at Reset or restore your Apple TV to its factory settings - Apple Support

Reset or restore your Apple TV (3rd generation) or earlier

1. Select Settings > General > Reset.
2. Choose one of these options:

• Reset All Settings: This option resets your settings, including your accounts and configurations.
• Restore: This option returns your Apple TV to its factory settings and installs software updates. This option requires Internet.

3.Keep your Apple TV plugged into power until the Reset process finishes. Then you can set up your Apple TV again.

Additionally, if for some reason you can’t access the menus anymore, then you may restore through a computer:

Restore your Apple TV - Apple Support

- Take note that some models need to be powered on their own at the indicated moment.

- Take note that the USB cable needs to support data transfer; not any charging cable will do.