You can add a Blink to your favorites in two ways:
1. From the 'For You' screen, navigate to your library.
2. Click the 3 dots next to the Blink you would like to add as a favorite.
3. Select 'Add to favorites'.
When you finish a title you can scroll to the bottom of the 'Final summary' page and add it to your favorites from there by clicking on the heart next to 'Favorite it'.