An owner can only be marked as the designated reviewer on a change order at the Prime Contract Change Order (PCCO) tier in Procore. To learn how to approve or reject a PCCO, see Approve or Reject a PCCO.
If you want the owner to review the change order at an earlier tier (at the Potential Change Order or Change Order Request) level, you can email them the PCO or COR which they can then respond to. You will see their responses logged in the Emails subtab of the PCO or COR in Procore. See Email a PCO to learn how to email forward a potential change order.