Hello @atjonesen,
Thanks for asking. 
Please note that the customization you are looking for falls outside scope of support we offer as it requires custom development. However, I could point you in the right direction with the understanding that it would ultimately be your responsibility to take it from here.
Before proceeding, I’d advise that you setup a child theme. This allows you to make code changes that won’t be overwritten when an X update is released. After your child theme is setup, please review how we recommend making template changes in Customization Best Practices.
Upon setting up the child theme, kindly add following code in child theme function.php
file:
// Social Output
// =============================================================================
if ( ! function_exists( 'x_social_global' ) ) :
function x_social_global() {
$facebook = x_get_option( 'x_social_facebook' );
$twitter = x_get_option( 'x_social_twitter' );
$google_plus = x_get_option( 'x_social_googleplus' );
$linkedin = x_get_option( 'x_social_linkedin' );
$xing = x_get_option( 'x_social_xing' );
$foursquare = x_get_option( 'x_social_foursquare' );
$youtube = x_get_option( 'x_social_youtube' );
$vimeo = x_get_option( 'x_social_vimeo' );
$instagram = x_get_option( 'x_social_instagram' );
$pinterest = x_get_option( 'x_social_pinterest' );
$dribbble = x_get_option( 'x_social_dribbble' );
$flickr = x_get_option( 'x_social_flickr' );
$github = x_get_option( 'x_social_github' );
$behance = x_get_option( 'x_social_behance' );
$tumblr = x_get_option( 'x_social_tumblr' );
$whatsapp = x_get_option( 'x_social_whatsapp' );
$soundcloud = x_get_option( 'x_social_soundcloud' );
$rss = x_get_option( 'x_social_rss' );
$output = '<div class="x-social-global">';
if ( $facebook ) : $output .= '<a href="' . $facebook . '" class="facebook" title="Facebook" target="_blank"><i class="x-icon-facebook-square" data-x-icon="" aria-hidden="true"></i></a>'; endif;
if ( $twitter ) : $output .= '<a href="' . $twitter . '" class="twitter" title="Twitter" target="_blank"><i class="x-icon-twitter-square" data-x-icon="" aria-hidden="true"></i></a>'; endif;
if ( $google_plus ) : $output .= '<a href="' . $google_plus . '" class="google-plus" title="Google+" target="_blank"><i class="x-icon-google-plus-square" data-x-icon="" aria-hidden="true"></i></a>'; endif;
if ( $linkedin ) : $output .= '<a href="' . $linkedin . '" class="linkedin" title="LinkedIn" target="_blank"><i class="x-icon-linkedin-square" data-x-icon="" aria-hidden="true"></i></a>'; endif;
if ( $xing ) : $output .= '<a href="' . $xing . '" class="xing" title="XING" target="_blank"><i class="x-icon-xing-square" data-x-icon="" aria-hidden="true"></i></a>'; endif;
if ( $foursquare ) : $output .= '<a href="' . $foursquare . '" class="foursquare" title="Foursquare" target="_blank"><i class="x-icon-foursquare" data-x-icon="" aria-hidden="true"></i></a>'; endif;
if ( $youtube ) : $output .= '<a href="' . $youtube . '" class="youtube" title="YouTube" target="_blank"><i class="x-icon-youtube-square" data-x-icon="" aria-hidden="true"></i></a>'; endif;
if ( $vimeo ) : $output .= '<a href="' . $vimeo . '" class="vimeo" title="Vimeo" target="_blank"><i class="x-icon-vimeo-square" data-x-icon="" aria-hidden="true"></i></a>'; endif;
if ( $instagram ) : $output .= '<a href="' . $instagram . '" class="instagram" title="Instagram" target="_blank"><i class="x-icon-instagram" data-x-icon="" aria-hidden="true"></i></a>'; endif;
if ( $pinterest ) : $output .= '<a href="' . $pinterest . '" class="pinterest" title="Pinterest" target="_blank"><i class="x-icon-pinterest-square" data-x-icon="" aria-hidden="true"></i></a>'; endif;
if ( $dribbble ) : $output .= '<a href="' . $dribbble . '" class="dribbble" title="Dribbble" target="_blank"><i class="x-icon-dribbble" data-x-icon="" aria-hidden="true"></i></a>'; endif;
if ( $flickr ) : $output .= '<a href="' . $flickr . '" class="flickr" title="Flickr" target="_blank"><i class="x-icon-flickr" data-x-icon="" aria-hidden="true"></i></a>'; endif;
if ( $github ) : $output .= '<a href="' . $github . '" class="github" title="GitHub" target="_blank"><i class="x-icon-github-square" data-x-icon="" aria-hidden="true"></i></a>'; endif;
if ( $behance ) : $output .= '<a href="' . $behance . '" class="behance" title="Behance" target="_blank"><i class="x-icon-behance-square" data-x-icon="" aria-hidden="true"></i></a>'; endif;
if ( $tumblr ) : $output .= '<a href="' . $tumblr . '" class="tumblr" title="Tumblr" target="_blank"><i class="x-icon-tumblr-square" data-x-icon="" aria-hidden="true"></i></a>'; endif;
if ( $whatsapp ) : $output .= '<a href="' . $whatsapp . '" class="tumblr" title="Whatsapp" target="_blank"><i class="x-icon-whatsapp" data-x-icon="" aria-hidden="true"></i></a>'; endif;
if ( $soundcloud ) : $output .= '<a href="' . $soundcloud . '" class="soundcloud" title="SoundCloud" target="_blank"><i class="x-icon-soundcloud" data-x-icon="" aria-hidden="true"></i></a>'; endif;
if ( $rss ) : $output .= '<a href="' . $rss . '" class="rss" title="RSS" target="_blank"><i class="x-icon-rss-square" data-x-icon="" aria-hidden="true"></i></a>'; endif;
$output .= '<a href="Second_facebook_URL"><i class="x-icon-facebook-square" data-x-icon="" aria-hidden="true"></i></a>';
$output .= '</div>';
echo $output;
}
endif;
You need to edit (Second_facebook_URL)
following like in above code to add new Facebook link:
$output .= '<a href="Second_facebook_URL"><i class="x-icon-facebook-square" data-x-icon="" aria-hidden="true"></i></a>';
Thanks.