How to add social icons to Storefront nav menu

// =========================================================================
// ADD SOCIAL ICON TO NAV MENU
// =========================================================================
function wdm_add_menu_items( $menu, $args ) {
    // check if it is the 'primary' navigation menu
    if ( 'primary' === $args->theme_location || 'handheld' === $args->theme_location)
    {
      // add the search form
      ob_start();
      $menu  .= '<li id="menu-item-5000" class="menu-item menu-icon">
                    <a target="_blank" href="">
                        <i class="fab fa-instagram"></i>
                    </a>
                </li>
                <li id="menu-item-6000" class="menu-item menu-icon">
                    <a target="_blank" href="">
                        <i class="fab fa-facebook-f"></i>
                    </a>
                </li>
                
                ';
      ob_get_clean();
    }
    return $menu;
}
add_filter( 'wp_nav_menu_items', 'wdm_add_menu_items', 10, 2 );