Self registration to a closed event using a link forwarded by email

Hello!
Our work conference is limited to pre-registered participants (by csv upload) who have been forwarded access via an emailed link directly from the Zoom Events platform.

After testing we noticed you can forward the sent email (link) to an outside person and they can self-register by accessing the join button and requesting a code.

How do I delete this self-registered option?

Thanks 🙂