If your purchase order was rejected, you can review its details, edit them, and resubmit the purchase order. A rejected purchase order includes the reason for rejection. See Viewing rejection reason. This will help you understand what to change so the next time the purchase order is approved.
You might want to change an approved purchase order. For example, another supplier offers better payment terms. Then, edit the purchase order details accordingly and post the order. If the order still meets the approval process condition, its approval status is reset to Approval required. This indicates you must resubmit the order for approval.
Resubmit a purchase order for approval in the same way as you submit it. See Submitting purchase order for approval.