In order to enable the wizard, you must first open a SeamlessDoc in Editor Mode. You can do that from the Lobby by clicking on the Form Name of a SeamlessDoc. It will open automatically in the SeamlessDoc Editor. Your screen should be similar to the one below:

Under the Form Name, you'll find the Editor Toolbar, and for the wizard, you should click on the Add Ons menu.

Select "Enable Wizard" and you will be redirected to the Form Editor as you'll now be able to add Form Elements to your SeamlessDoc.