Form Builder is intended for building your forms, not editing them.
if you have already created the form, you should add the Validation, Insert, File Upload or other behaviors manually.
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.