When a Purchase Order (PO) is deleted, it cannot be brought back. However, when a PO is deleted the items in that PO should be sent back into the Needs Purchasing Report to allow you to add them to a new PO. . (unless the items have been marked as Awarded).
You also should be able to find them on the Recognition Report for the given time period. You will need to unapprove / unaward them. See: https://help.scoutbook.scouting.org/knowledge-base/how-can-i-un-award-all-advancements-awarded-between-a-time-period-sb/