Hello Sapna,
I am not sure what exactly you are asking. Are you looking for a FM which forcefully changes the status to Closed for PO or you are asking when actually the PO gets closed if that's the query then I guess when the Final Delivery is checked then it says PO is closed now as no further action can be done. It also says that all the payments has been done to the vendor . And now no further action to be taken.
Thanks
gaurav gautam