How to resume approval process for a large number of POs that got stuck?

Summary:

Need to resume approval process for a large number of POs

Content (required):

Our approval flows are setup using approval groups and are generally associated to specific worker IDs.

One of the managers left the company and a large number of POs (+100) were left unapproved. The only solution we know to resume the approval process is to withraw orders and send again for approval, but we are looking for a different solution as it would be very time consuming to withdraw more than a hundred POs one by one. Is there a scheduled process we can run? Or any other solution we can try?