Add custom class to wordpress navigation

Please write below code in functions.php

add_filter('nav_menu_css_class', 'current_type_nav_class', 10, 2);
function current_type_nav_class($classes, $item) {
// Get post_type for this post
// Go to Menus and add a menu class named: {custom-post-type}-menu-item
// This adds a current_page_parent class to the parent menu item
if( in_array( $post_type.'-menu-item', $classes ) )
array_push($classes, 'current_page_parent');

return $classes;

}