What kind of edits are you trying to make to the form?
You should use Dreamweaver for editing the form.
if you ned to edit the Spry settings, select a form element, then click the blue bounding box around the element to trigger the spry settings in the properties inspector.
if you need to edit the server validation, then open the server behaviors panel, double click the server validation behavior to make your changes.
The Data Assist wizard is used for creating the pages. once created, Dreamweaver is the platform for editing the pages