Google Play Music & TV for Android has been updated to version 3.2.25 which brings a new Wish List feature to the app. The 'Wishlist' can be accessed on the "Watch Now" screen or through the slide-out navigation bar on your app.
The update is just rolling out, so it maybe a few days before it reaches your device. You can download the latest version through the Google Play Store or using the following link:
If you dont want to wait for the official update through the Google Play Store, you may want to consider downloading the official APK file by following the source link
source - Android Police