Favicon or site icon is the symbol that show in top left of the browser. It is the identity of your website when user visit may sites in different tabs then they can easily recognize your brand identity by the favicon.
Follow the steps how to add/ edit the favicon:
Step1: First Login to your WordPress website admin end then go to Appearance => Customizer
Step 2: Then go to Site Identity
Step 3: Now you will get two buttons to Remove or Change favicon image.
Then save and refresh in home page you will get the favicon. Sometime for browser cache it may take some time to appear.