Email at Pre-registration

Hi zoom community,
I have a question about customizing webinar registration.
My organization presends workshop for Pharmacists.
Credit will be given to pharmacist who attend the workshop, but it must be recorded that they have attended.
but If someone registers using another person's email address, the information previously registered using that email address will be overwritten.
Is there a way to alert someone when someone registers an email address that is already registered ?