How do I email a reminder to all RSVP submissions in the system?

We do not have a built-in option to notify the form users.

You might consider downloading a list of the email address from submissions page, and then emailing them manually.

How to Download Form Submissions as Excel/CSV

Alternatively, it might be possible to integrate the form with Mailchimp email marketing service and email those users from Mailchimp.

How to Integrate with MailChimp

If you need any further assistance, please let us know.