If you are using a PO then it is not possible to amend work. Instead, you can cancel and create a new piece of work with the supplier (with a new PO, as necessary).
However, if you are using our dynamic scope of works tool, you can update work anytime before the work is completed. To update the work, first navigate to the specific work item you would like to view.
From here select the "Deliverables" tab. In the "Deliverables" section, if you are using a dynamic scope of works then you can delete / add new requirements to the list.
Any changes will be documented and sent to your supplier for them to accept.