Can I use any lounge in the airport in first class?

You can't. There is a special VIP room in the first class, and you can use the VIP room in the airport. In order to prevent the confusion of airport personnel, you can only rest in the designated VIP lounge, and you can't use any lounge in the airport. In the VIP lounge, you can enjoy free drinks and snacks, and provide free massage with massage chairs.