You can download the logo pack from facebook with link below
https://www.facebook.com/brand/resources/facebookapp/logo
alternatively
You can use font awesome by adding this cdn
/* Add to head, this script is from font-awesome.icon */
<link href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/5.13.0/css/all.min.css" rel="stylesheet">
/* Add this to where to need the icon in your html */
<i class="fa fa-facebook-square" aria-hidden="true"></i>