How to update a hidden field from the database before UE sends the form

I have implemented a send password form for UE to send. I followed the threads so I only send the form fields I want and that all works.

I added a hidden field to the form to receive the password from a record set after looking up the email address.

The problem is I need things to happen in the following sequence,
1. Take the email address from the form after the submit button is pressed
2. Have the record set updated based on the email address
3. Update the hidden field with the password
4. Have UE send the email.

Is there a way to sequence this with another hidden value which I update with each step, or is there a more elegant way to do this?