The DOGTV app is only available on 4th & 5th Generation (4K) Apple TV’s.

If you have the 4th Generation AppleTV (Sept. 2015) or the 5th Generation 4k Apple TV (Sept. 2017), then you can download app the DOGTV App from the App Store.  Unfortunately 3rd generation and older Apple TV’s do not have an App Store and there is no way to install 3rd party apps on these models.

To check the model of your Apple TV go to: Settings > General > About