Add the first snippet into the functions.php and the second snippet into one of your wordpress template files. This snippet will allow you to return a page ID by the page name. Don’t forget to change PAGE_NAME to the name of the page you would like to return the ID of.
$page_name_id = $wpdb->get_var("SELECT ID FROM $wpdb->posts WHERE post_name ='".$page_name."'");
$the_page_id = wds_get_ID_by_page_name('PAGE_NAME');