Hello Anu Gottumukka,
BAPI_PO_CHANGE is executing for each item and after execution of BAPI for each item then check the IT_RETURN table .
Loop the it_return table and IT_RETURN -TYPE field contains the message status and Message type will be S Success, E Error, W Warning, I Info, A Abort.
Based on the out come of IT_RETURN -TYPE you capture the error items and update in the respective table and display it.
Thanks and Regards,
Madhukumar L