I found a solution,
I have create an input width menu_order as value
<input type="texte" name="menu_order" value="<?php echo $post->menu_order; ?>"/>
and when i update acf_form();
I launch a function :
add_filter('acf/pre_save_post' , 'my_pre_save_post' );
function my_pre_save_post($post_id) {
$menuOrder = $_POST['menu_order'];
$post = array(
'menu_order' => $menuOrder
);
$post_id = wp_update_post( $post );
// Save the fields to the post
do_action( 'acf/save_post' , $post_id );
}