hi.. we are staying at ashoka hostel in Hong Kong. can i take the free shuttle bus to mira hotel then just walk?

I am not very clear about the situation of the free shuttle bus of the mira hotel. If they have the shuttle buses, you can take them.
As far as I know, your hotel is in Chung King Mansion, so you can take the airport shuttle bus A21 Middle Road, Nathan Road Station and then walk to reach your hotel.