The system allows you to edit the PO you have requested unless any of the approvers has not approved/rejected.
1. Go to PO page. Search for the PO # which you wanted to edit. If its not yet approved by any of the approvers, system will show the Edit Request PO button at the right end of same PO record row.
2. Click on that button, it will open the Edit Request PO page. Make the required changes and you can also send chat message to approvers for any additional information and click on submit button.