How to work with changes in Purchase Order in Inbound Purchase Order EDI

Hello, My requirement is as follows Supplier has suggested that he would be able to supply the particular order on a new date. he sends this data through EDI. How will this data be updated in Purchase Order through EDI. The field to be updated in Promised Delivery date (PDDJ) I tried using R47021 EDI process 855 and R47141 EDI process 865. But in both process, only status of the Purchase order is updated and not PDDJ field. Could you please advice what would be the correct EDI to be used.

Regards Jiten Patel