Cancel a line in an internal requisition

Hi All,

I created an internal requisition sourcing from one of the inventory org. There were 3 lines in the IR. The IR was converted into an Internal sales order.  The first 2 lines in the Sales order was shipped and not the 3rd line. So went in and cancelled the 3rd line in the SO. Now i am not able to cancel just the 3rd line in IR. I can only cancel the IR at the header, which means i cancel all the 3 lines in the IR.

Can someone pls tell me how i can cancel just the line in an IR.