Get the test build
Yuna is available to approved testers. Use the installation link you received and the Google account enrolled in that test. An internal-test link and a closed-test link are different. The app is not yet publicly released.
On your TV
Use a supported Google TV or Android TV device. Install the TV build and navigate with your remote. Sign in with the same Yuna account as on your phone.
After installation
Create or sign in to your account, choose a profile and add a source you are authorised to use. You can skip adding a source and return to it later.