Assign a device that was serviced or replaced in Apple Business Manager
Service a device
If you have an iPhone, iPad, iPod touch, or Mac enrolled in Apple Business Manager and that device is serviced, you should unassign the device from the MDM server. When the device is returned, you can reassign it to the same MDM server.
Replace a device
If you replace an iPhone, iPad, iPod touch, or Mac currently enrolled in Apple Business Manager through an Apple Authorized Service Provider, the replacement device is usually also available for enrollment. You can manually assign the device to a server using your order number. To find replacement devices, search for order numbers that begin with the letter R.
If you replace a device that was assigned to a specific mobile device management (MDM) server, the replacement device is automatically assigned to the same server.