functions.php

//* Add menu item to header-right menu
add_filter( 'wp_nav_menu_items', 'custom_nav_item', 10, 2 );
function custom_nav_item( $menu, $args ) {
    //* make sure we are in the primary menu
    if ( ! has_nav_menu != $args->theme_location  ) {
        return $menu;
    }
    //* see if a nav extra was already specified with Theme options
    if ( genesis_get_option( 'nav_extras' ) ) {
        return $menu;
    }
    //* append your custom code
    $menu .= sprintf( '<li class="menu-item">%s</li>', __( '<a href="#" class="search-toggle"><span class="dashicons dashicons-search"></span></a>' ) );
    return $menu;
}