Setting up a favicon on your website is not as easy as you might think.
But you can do this using
Favicon by RealFaviconGenerator wordpress plugin.
Favicon by RealFaviconGeneratorWordPress Plugin
Search 'Favicon by RealfaviconGenerator' in [Plugins] -> [Add New] page and install it.
Go to [Appearance] -> [Favicon] page and select logo which you want to ganerate as a favicon.
Generate favicon button to start generate. You will be redirected to generation page.
Choose options which you want to apply, and click
Generate your Favicons and HTML Code button on the bottom to apply it.
You will be comeback to your website, and you will see the favicon in your browser.