To access Review Builder you would click on Review Tab along the top menu. Once in the Review Builder tab, you can make your selection on the left-hand menu to which type of form you would like to edit.
To edit a Form or Template you would click on the pencil icon to the right side of the form name:
Now that you are in the edit mode of the Review Form you would click on Edit Form which would then take you to the HTML version of the form.