• Insert the Elmo's banner snippet on every website's page (link to the official documentation)
• Create the "Edit preferences button" in the website's footer as usual.
• From the top navbar, select "Advanced-> Enable developer options" (it's a temporary option needed in order to setup our configuration)
• Scroll down until you reach the footer, and click on the "Edit cookie preferences" mentioned above: take note of the code, similar to "#text1234", that will be shown once we highlight the element.

At this point a screen will open below the footer of the page with various options, from the right side panel we select "Open file masterPage.js".

• We add to the file the following code: #text1234 is the code we noted when clicking on the aforementioned element.
  
  $w('#text1234').customClassList.add("elmo-show");
• Going back to the top bar, we select "Advanced-> Disable developer options" to restore the original UX.

Now the element created by Wix editor has a custom class that, once the banner is loaded, will allow any visitor to update their preferences.