At times, you may need to install a specific app or book onto certain devices.
To achieve this you’ll need to create new groups just for those apps or books, then add specific users or devices into those groups.
For example, create a group called Apps or Books somewhere near the top of your hierarchy, inside that group create a sub group specifically for each app or book, install only one app or book into each group.
Then simply add the specific user or device into the required groups.
A logical overview:
How it would look in the UI: