Shuttle bus service in hong kong

Hi, Char. I think you may misunderstood the free shuttle buses.
The shuttle buses are operated between the Kowloon Station and the Cityview Hotel. So you need to take the airport express line to Kowloon Station and then take the free shuttle bus K5 to the hotel.

From your hotel, you can also take the free K5 to Kowloon Station and then take the airport express.
A cheaper method to your hotel may be the airport shuttle bus line A21 and you can take this line to reach Man Ming Lane, Nathan Road Station and then walk to your hotel. The fare is around 33HK$.