Check for duplicate RSVP

Hello community,
I have a RSVP form which asks for user to enter user name, whether a user will attend or not, and number of guests accompanying the user to this party. This is working well - except, I just realized that I did not built in a check that prevents a user from RSVP’ing twice. Any thoughts on how this could be accomplished?
I was thinking that I check the current logged in user’s email with all the users email in the USER data type and disable the RSVP form if there is a match. I am not sure how to do that?

This is because - when I am asking a user to sign up, I am only asking for user’s email, and password. And that info flows into the USER data type. Whereas, when I am asking a user to RSVP, I am not asking for email, but just the name. I thought I will be able to figure it out - but using the name in the RSVP data and email used to log in. But apparently I am not able to figure this out so I need help.
How do I check user’s email from USER data type and take the corresponding name, and check that name with the RSVP data type?

Just check whether the current User already has a RSPV (i.e. do a search for RSPVs created by the current User)

Thank you!