Restrict to Edit Purchase Order

Hi All,

We Are utilizing SAP s4 HANA Public Cloud, we are facing immoderate challenge. While utilizing "Create Purchase Order - Advance" app erstwhile PO oregon STO approved, strategy inactive permits changing to STO oregon PO. This causes disruption to our company's operations.
How tin we forestall users from editing authorised STOs oregon POs?

Regards,

Zeeshan Baig