When you go to the details of a VPP app, You can see the total, available and used VPP licenses.
When clicking on "Total", "Available" or "Used" it will bring you to the overview of active licenses in your environment.
Here you have 2 options: you can revoke a single license (if that is possible) and you can synchronize all licenses with the current scope.
Revoking a single license will do exactly what you expect, revoking that license with Apple VPP and removing it from the list. Also, the license count should be updated directly.
Synchronizing all the licenses will look at the current scope, determine which devices and/or users need a license and make sure licenses are given to all these. It will also revoke licenses from known users and devices that are no longer in scope!
There is one other change in the way the teacher app deploys VPP applications. Before this change it would simple assign a license and give the InstallApplication command to the iPad. This no longer works, since resyncing the licenses will remove that license, since it is not in scope. In this new version, assigning a VPP app in the teacher app will explicitly add the devices to the scope of the app. Unfortunately the UI for this is not done yet (so you can’t retract those), but expect this in the next update!