Meeting Mojo operates on the understanding that any delegate who is on the system has previously consented to their data being uploaded and has agreed to join the 1:1 meetings. As a result, there is no opt-out and your delegates need to ask you to delete their entry if they find they are unwilling to participate. It's possible to provide an opt-out only if your delegates register themselves on your Meeting Mojo site. Create a Group option that is not permitted to book 1:1 meetings which they must select on registration.
Learn more about creating and organising Groups by visiting this article.