code: public function process(array $event)
      {
          $event = parent::process($event);
  
          $event['uniqueId'] = substr($event['extra']['requestId'], 0, 7);
          unset($event['extra']['requestId']);
  
          return $event;
      }
docs: Processes a log message before it is given to the writers
  
  @param  array $event
  
  @return array