How to hide the FROM Email address in the PO Output for Communication E mail notification?

When a PO is approved an email notification is sent to the supplier with PO as Attachment.

By default the FROM email address is displayed on the email (This is the Buyer I think) but we want to hide it . How can we do this?

Note- the WF seems to different if the email is sent from PO Super User > PO Summary > Tools > Communicate as this uses PO Approval workflow root activity "EMAIL_PO_PDF"

If the email is generated from the approval of the PO it uses POAPPRV_TOP.

Its the latter that we want to customise and hid the FROM Email address.