You can delete a transport domain if:
If you want to delete a transport domain, you must delete the TMS configuration for all systems in the transport domain.
Ensure that no transports are performed while you delete the transport domain.
To delete the transport domain:
For more information, see Deleting a SAP System from the Transport Domain.
The TMS is deactivated for systems that had the TMS configuration deleted.
You can now rebuild the transport domain.