Editing email message after adding signature fields

There is a sequence of steps for preparing to send a document for signature.  On the first page, you add recipients, edit the message body, add the file, and then click the checkbox for preview and add signature fields.  I have been unable to find any way to return to the message body to edit it after clicking "preview and add".   The only choice available seems to be to discard the preparation and start over from the beginning, sometimes discarding significant work.

So my question is:  Does anybody know how to edit the email message after adding signature fields?

Thanks!

Tom