Like others have mentioned, this feature is not in ISC as of yet.
I’ve had this same use case before and used a powershell script to automatically reassign users based off of the ownership details, but this comes with some quirks you’ll have to fix. For example, disabling notifications and explaining why things are reassigned on the logs instead of being set there by default.
I think the easiest solution for you would be to wait for the upcoming Next Generation Certifications release that is set to come out here in the new few weeks. You’ll need to contact your CSM to have your tenant enrolled early. This solution is out of the box and handles the requirement like IIQ. See the product news updates below for up to date release details.