How can I send an email trigger to a contact if I only know their External Data Reference?

I am embedding Qualtrics surveys into the EdX platform and can only send the user ids of the people filling out the surveys as embedded data through the URL. I can export these ids from EdX and import them to a contact list in Qualtrics with their corresponding emails and names, using the External Data Reference field for the EdX user id. However, I cannot figure out how to take this embedded data and obtain their name and email from the contact list to send them a confirmation email. Can this be done? Thank you!