How to correct the PO Line schedule that is matched in Purchase Orders?

We have a voucher created sourced from PO online (PPO). Purchase Order is Partially matched with the three of its lines schedules are updated with Match_Status_Ln_PO as "Fully Matched". Hence the matched schedules are not showing up in the Voucher - Copy Worksheet page (Invoice information tab). As the schedule is matched it's shown in the Copy Worksheet page. The user wanted to correct the schedule that are matched. How can this be corrected ? Thanks, Geetha