BAPI determine FM-document timing in PO

Hi experts ,

I am facing an issue that I should change the FM-document created time from first time saved by the creator to final approving in PO .

I was told that i should use BADI : ME_COMMTMNT_PO_REL_C

and use a BAPI in order to determine the timing .

could you tell me what is the procedure of using this BADI ,and which BAPI should i use to change the document created timing ?

Thanks in advance !

Keivn