iOS devices enrolled through Apple Business Manager (ABM/ASM), must be assigned users in order to allocate devices. Users can be assigned to each device either individually or in bulk by adding a CSV with the user details. This process can be time consuming and cumbersome, when the device user is to be reassigned. MDM resolves this by automating user assignment for devices enrolled through ABM as explained below:
Don't know about ABM? Learn how to enroll devices using ABM under 4 minutes here.