1.go to Appearance » Customize and click on the ‘Site Identity’ tab
2.click on the select file button and then upload the image you want to use as site icon.
3.Adding Favicon to Older WordPress (4.2 or below)
Upload your favicon to your website’s root directory using FTP.
Paste this code into your theme’s header.php file.
<link rel="icon" href="/favicon.png" type="image/x-icon" />
<link rel="shortcut icon" href="/favicon.png" type="image/x-icon" />
4.You are good to go.
If your theme does not have a header.php file, or you can not find it, then don’t worry we have a plugin for you. Install and activate Insert Headers and Footers plugin. After activating the plugin go to Settings » Insert Headers and Footers and paste the code provided above in the header section and save your settings.