Might be you already tried this: If the entitlement owner you want to certify then why not opting the Certification from search using the query → owner.name:“Admin 1” ← this should allow you to select all the entitlements that Identity owns and then certify it by selecting any one identity from the list of holders of that entitlement to direct the Owner to Certify by selecting him as a INDIVIDUAL reviewer.
This should solve your use case needs for revalidating the needs of that entitlement.