A Favicon (also known as a website icon, tab icon, or bookmark icon) is a small icon that represents your website and provides a shortcut wherever the icon appears.
Access favicon settings with the theme editor
Once you have an image you want to use, go to Customize > Theme settings > Favicon and upload it by clicking Select image. If you have already uploaded the image to the Files admin, select the image from your media library.
Images should be either 16 x 16px or 32 x 32px.