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

Click here for the next steps