Mass Re-assign PO

An employee has retired and I want to re-assign all of her current, in-process PO's to another person.  I don't want to replace the history for the retired person, only re-assign so that the POs continue to move forward.

Also, do I need to know the exact PO numbers for re-assignment or can I mass-grab all of them that haven't been closed yet?

What is the best way to do this?

Thanks