display 3rd level of menu only after clicking on its parent in the 2nd level

i have a three level menu and would like the 3rd level only appear when i click on its parent in the second level.

here is my website:https://thelondonlife.de/

i would like “level3″and “another level3” only to be displayed after i click on “kontakt”

can anybody tell me how i have to change my functions.php please?

<?php
}
if ( function_exists(‘register_sidebar_widget’) )
register_sidebar_widget(__(‘Links’), ‘widget_techdesigns01_links’);

function list_subpages_techdesigns01($return = 0) {
global $wpdb, $post;
$current_page = $post->ID;
while($current_page) {
$page_query = $wpdb->get_row(“SELECT ID, post_title, post_parent FROM $wpdb->posts WHERE ID = ‘$current_page'”);
$current_page = $page_query->post_parent; }
$parent_id = $page_query->ID;
$parent_title = $page_query->post_title;
if($wpdb->get_results(“SELECT * FROM $wpdb->posts WHERE post_parent = ‘$parent_id’ AND post_status = ‘publish'”)) {
echo'<div class=”menuheader”></div><div class=”menucontent”><h5 class=”menunav”><span>Navigation</span></h5>

‘;
$html = wp_list_pages(“child_of=$parent_id&depth=$depth&echo=”.(!$return).”&title_li=0&sort_column=menu_order”);
echo’

</div><div class=”menufooter”></div>’; }
if($return) {
return $html;
} else {
echo $html; } }
?>