If the device is still has access to and can connect to the MobiControl instance then you can issue an Unenroll from the MobiControl server which I believe should allow you to remove the agent. I don't believe you can otherwise configure the device or do anything manually at the device level to remove the Device Owner status of a DPC and that is pretty much by design. One of the flaws of Device Administrator based management is that end users were potentially able to manually remove the DA privilege from MDM agents. Android Enterprise Work Managed devices managed under DO however do not offer this option to manually remove it at the device level because that would basically defeat the purpose of Device Owner managing the device.