Generate Navbar In WordPress

You could use Javascript to move the Submenu items where ever you please.

<script>

    jQuery(document).ready(function() { 
        (function ($) { 
            $('.sub-menu-new').after( $('.main-menu') );        

        })(jQuery);
    });

</script>

OR…

You could take a look at the wp_nav_menu_objects filter hook

It could allow you to do a check against every menu item and maybe store the submenu items somewhere else to be displayed elsewhere

add_filter( 'wp_nav_menu_objects', 'your_wp_nav_menu_items', 10, 2 );
function your_wp_nav_menu_items($items, $args) {
    if ($args->theme_location == 'primary'):
        foreach($items as $item):
            //only display items you want; and store the other items for later output
        endforeach;
    endif;
}

BUT I WOULD NOT WASTE TIME DOING THAT. Why don’t you just make more than one menu and output them where you please?