You have set the "id" attribute for the target element.
In the builder, you click on "HTML editor" icon and in the HTML code, for the first element add the "id" attribute. If the first element is a "div" tag then you add the is as follows:
After that, for the menu item, set the URL link to "#" followed by the id value of the element. ie. "#YOUR_UNIQUE_ID_HERE" (without the quotes, of course)