How to have approval process while reducing the unit price of item in the approved standard PO for s

Hi All,

User created PO and submitted for approval. Since he  don’t have approval limit, it had gone to approval process to get it approved. Then user reduced price of the item after negotiation with supplier .When he submitted for approval, the document has got self-approved. User is expecting that the PO should go to approval process instead of self-approval.

Created standard Purchase order and submitted for approval. Since the buyer don’t have approval limit, it followed the approval hierarchy process.

When all the approves approved, document status changed to approved

Reduced the unit of price of item A  from 1523 to 751 and the document status went to Requires Reapproval. Also document revision created