Auto-populate Participants (name, email, etc.) into web form after Participant 1 enters those values

I have a web form agreement in Adobe Sign for which all participants are manually designated/inputted by Participant 1.  After they complete their portion of the form and hit 'click to sign', they are prompted to enter the first name, last name, and email for participants 2 and 3.

How do I auto-populate the information Participant 1 entered into the form after they complete their portion? I see how it can be done if you customize the senders in document setup, but this is a web form and I do not enter any information about the senders before sending it out.