public function mark_major_change() {
        global $DB;

        // Clear old reset and completion notes.
        $DB->delete_records('user_preferences', ['name' => self::TOUR_LAST_COMPLETED_BY_USER . $this->get_id()]);
        $DB->delete_records('user_preferences', ['name' => self::TOUR_REQUESTED_BY_USER . $this->get_id()]);
        $this->set_config('majorupdatetime', time());
        $this->persist();

        return $this;
    }