How do you cancel a Sales Order Line which IS IN CLOSED STATUS.

Hello ,

I have situation where :

A Sales Order was created with 10 lines. This created a Requisition and a PO.( PO # 5555563644 )
Later a new Line was added to the Same Sales Order and it created a Different Req and a PO ( PO # 5555563731 ). This was added as a replacement to Line # 2 on the Preevious PO( PO # 5555563644 )
Both the Sales Orders are Closed by OMCLOSE Process.
Both the Sales Orders are shipped and billed..
User has cancelled line # 2 on on the Original PO # 5555563644 .
How do we cancel the Coressponding Sales Order Line.
What are the Tables that need to be considered if we have to do a SQL UPDATE / SQL Delete.