Smart DNS is a technical solution that allows you to bypass geographical restrictions and access blocked websites. To use it, you need to subscribe to a VPN provider that offers this feature and find out your Smart DNS addresses. After that, follow this path:
Go to Settings on your Apple TV - Network (bottom of the page) - press the WI-FI button - select the network you're connected to - press "Configure DNS" and go for manual configuration - Enter one of the DNS addresses provided by your VPN - press "Done" - Restart your Apple TV. That's it!