How can I access to to custom folder (GetDefaultFolder (6)) take me to the default inbox.

The following code sample should help you figure it out:

oOutlook = CREATEOBJECT( [Outlook.Application] )
oNamespace = oOutlook.GetNamespace( [MAPI] )
loRootFolder = oNameSpace.Folders(1)
FOR EACH loFolder IN loRootFolder.Folders
  ? loFolder.Name
NEXT 

Of course, this assumes that your custom folder is under Personal Folders. If it is under the Inbox, you will have to modify the code above accordingly.