A favicon is a file containing one or more small icons which will appear as your shortcut icon, website icon, tab icon, URL icon or bookmark icon.
To add a favicon
In the Left Sidebar of the settings menu, select Site Settings.
Under Favicon, select add image.
In the file manager, upload and select your favicon image.
Select the '+' icon to use the image.
Select the save button in the top left of the editor to save your changes.
Note: Please allow up to an hour for your favicon to propagate amongst your pages.