When a purchase order has been approved by amount the status becomes released. The vendor might bring changes such as delivery date. To bring these changes into the purchase order, it needs to be reopened again.
Then you can make the changes in the purchase order. then next step is to release the purchase order, but before that is has to go through the approval stage again and to be handled again.

The requested improvement is:
When the total amount of the purchase order has not been changed, the approval process will be skipped.
The check can be done to compare the current purchase amount with the latest posted approval, where the amount is stored.
The reason for the change is that approvers do not need to approve a purchase order they already approved, when the amount has not been changed