This definitely requires a child theme (which this theme has) if not already using it. But the easiest way would be to convert one of the other icons as a second facebook icons.
The files you would need to customize and into the child theme are:
- includes/theme-customizer.php (social stuff begins around line 566 for whichever one you change)
- style.css around line 464 (again, replace one of the social icons with the facebook one to give you a second icon
The rest will be up to you …
Fun hey! :woohoo: