Use external drive wirelessly
How do I configure Mountain Lion, Airport Extreme to remotely access that harddrive
MacBook Air (13-INCH, MID 2011)
Is the drive attached to the Airport Extreme?
If so, then you use the Applications -> Utilities -> Airport Utility to configure the disk and make it avaiable.
Once it is properly configured via Airport Utility it should show up in your Finder side-bar as something you can connect to and mount.
If this is not what you are talking about, please provide additional information about what you desire.