Navigation template

I found the solution.

I had to add this in functions.php :

add_filter('navigation_markup_template', 'my_navigation_template', 10, 2 );
function my_navigation_template( $template, $class ){

    return 
    '<footer>
        <nav id="nav-below" class="navigation" role="navigation">%3$s</nav>
    </footer>';
}

Source : http://wp-kama.ru/function/_navigation_markup