By default Freelancer enqueues its own minimal set of icons for use throughout the stylesheet and general design, but in cases where you want to override this functionality and add your own custom icons you can simply filter in your own custom icon URL by pasting and editing the following code inside your Child Theme’s functions.php file:
add_filter( 'freelancer_icons_url', function() { return get_stylesheet_directory_uri() . '/icons/css/custom-icons.min.css'; } );
Then of course be sure to match up your actual custom icon’s CSS file with the URL specified in your add_filter code.