You need to install Downloader by AFTVnews so you need to go to the Apps menu
Click Search for apps
Search for Downloader. You can use the keyboard or press the Google Assistant button and say "downloader"
This is the one you need to install. Once it is installed, DO NOT open it yet
Go to your Google TV device's Settings
Go to System
Click About
Go down to Android TV OS Build and click it SEVEN TIMES
Once you "become a developer", go back and select Apps
Go down to Security and restrictions
Click on Unknown Sources
Select Downloader
Toggle the switch to Allowed
Go back to the Apps section of your home screen and open Downloader