Editing Purchase Orders Created using Requisitions through the BWC

We are new to the Buyer's Work Center.  One of our procurement specialists' created a Purchase Order from a requisition in the BWC.  The individual then updated the line description.  Now the PO and the Requisition are showing as commitments against the project.  We cannot cancel the requisition since it is tied to the PO.  How do we get rid of that commitment?