WordPress 4.3 introduced a new “Site Icon” feature, which provides a user-friendly interface for adding a favicons to your websites. Icons are also used as app icons on mobile devices.
The Site Icon feature can be found by going to Appearance > Customize and selecting the Site Identity option.
Then click the Select File button and choose an image in the media library or upload a new file.
Icons should be a minimum of 512 pixels wide by 512 pixels tall. If the image is rectangular, WordPress will prompt you to select a square portion after uploading.