Deletion is an operation which should be performed with extra care, based on this - such procedures are not public and can be provided only by TAC.
Please open to us relevant service request and we will provide with a procedure to perform the desired maintenance.
There is one possible issue which could prevent automatic purge of inactive devices - if the database contains duplicate devices - and in this situation once again - SR should be raised.
If a device got deleted manually or automatically - if it will communicate with the server again - the system will not allow them to connect with error " Not found in PAT" error in server_messages.log.
Such device can be reinstalled or reconnected.
TAC can provide a reconnection procedure.