You must have Admin Level - Webmaster access to add a favicon to the website.
A favicon is an icon that appears in the browser's tab in which a website is loaded.
The size should generally be 32x32 pixels in the .png or .ico format. Create one for the site or generate one through a site like RealFaviconGenerator.
In the side menu, click Website Design.
At the top of the site, click General Settings.
Click the Website Favicon dotted line box and select the Favicon file from your device.
Click Save.
Refresh the page to see the favicon appear in the browser's tab.