The edit bottons won't show in the properties panel until you have applied CSSFormBuilder to the form on your page.
To do this, select the form on your page (make sure it's selected by clicking the form#formname on the elements bar that sits just above the properties panel) and then in DW menu bar, select Insert > WebAssist > CSS Form Builder > Insert Form.
You can then configure the design and contents of your existing form and add whatever validations you want.
Thereafter, you can re-enter the form at any time by using the edit buttons which willnow show in the properties panel.
If you just want to apply validation to an existing form but not change design or content, you can just choose Client or Server validation from the WebAssist CSS Form Builder Insert menu.