-------------------------------------------------
Use the following code if you are using PNG image
-------------------------------------------------
function add_favicon_png() {
$favicon_url = 'https://..favicon.png';
echo '';
}
add_action('wp_head', 'add_favicon_png');
-------------------------------------------------
Use the following code if you are using ICO image
-------------------------------------------------
function add_favicon_ico() {
$favicon_url = 'https://..favicon.ico';
echo '';
}
add_action('wp_head', 'add_favicon_ico');