Assign a device to a device management service
If you don’t choose to automatically assign newly added devices to a device management service when you add them, you can manually assign them to a service that links to Apple School Manager or Apple Business Manager.
Make sure you properly configure your device management service so that it contains enrollment settings and an enrollment profile for the device.
Sign in to Apple School Manager
or Apple Business Manager 
.Select Devices from the sidebar, then use the filter to show only “Devices added by Apple Configurator.”
If the device doesn’t appear in the list, you may need to refresh the list of devices before the newly added device appears.
You can now transfer the device to an existing device management service in Apple School Manager or Apple Business Manager. For more information, see:
After assigning the device to a device management service, you can restart it to enroll it in that service.