Change field when Save Process Order

Hello, I need to update the caufvd-cy_seqnr field in the creation or modification of the process order, I used the PPCO0007 exit, and it does not function(no update field) instead, I understand that it is because the order is still temporary, does anyone know how to modify it? How to modify the Sequence Num field of the Assignment tab automatically?? I appreciate the support