On the apps row of your home screen, go all the way left and click on Apps

Click Get more apps

Go to the magnifying glass icon to search

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 Android TV device's Settings and select Device Preferences

Go to Security & restrictions

Click on Unknown Sources

Select Downloader and toggle the switch to Allowed

Go back to the Apps section of your home screen and open Downloader

Click here for the next steps