If you want to remove a Primary Server that is designated as the MDM Server in your zone, then you must first remove the MDM role from this Primary Server. To remove the role, you need to:
Click Configuration on the left hand side navigation pane in ZCC.
Click Infrastructure Management > MDM Servers.
Select one or more MDM Servers and click Remove.
NOTE:If you have removed an MDM role from a server in the zone, then you can add it back only after 30 minutes from the time the role was removed.
Since mobile devices contact the MDM Server to which they are enrolled and if mobile devices are enrolled to a server that you have chosen to remove from the zone, then you will have to re-enroll these mobile devices to the zone using another MDM Server. Before re-enrollment, ensure that you delete the corresponding device objects in ZCC. However, if you are upgrading or replacing the MDM Server with another server, then the enrolled devices will automatically reconcile with the replaced server. Also, if you delete all the MDM Servers, then the push notifications configuration (APNs and GCM) will be automatically deleted.