code: public function submitForm(array $formValues) {
      $this->configFactory->getEditable('liveblog.notification_channel.liveblog_pusher')
        ->set('app_id', $formValues['pusher_app_id'])
        ->set('key', $formValues['pusher_key'])
        ->set('secret', $formValues['pusher_secret'])
        ->set('cluster', $formValues['pusher_cluster'])
        ->save(TRUE);
  
      if ($formValues['pusher_app_id'] && $formValues['pusher_key'] && $formValues['pusher_secret']) {
        $this->configFactory->getEditable('liveblog.settings')
          ->set('notification_channel', 'liveblog_pusher')
          ->save(TRUE);
      }
    }
docs: {@inheritdoc}