Serial Number Returned To Supplier Flag

We rejected serialized inventory from a DMR, but did not check the “RETURN TO SUPPLIER FLAG”… SHipped the inventory back to the supplier for rework. Now the supplier shipped them back but we cannot receive due to the serial number being already used.

Does anyone know how to receive the serials back into the system on the new PO? What change to the serial number does the “RETURN TO SUPPLIER” flag on a DMR rejection make - how can you fix it?