in VB6, to specify this attribute for the NewEnum method you use the "Procedure Attributes" menu item. In VBA there's no similar option, however you can achieve the same result by either:
1) create the collection class (I assume that's what it is) in VB6, then take the resulting ".cls" file and import into your VBA project.
2) from VBA, export the class module and open it in a text editor such as notepad. Modify the function so that it reads:
Public Function NewEnum() As IUnknown
Attribute NewEnum.VB_UserMemId = -4
Set NewEnum = myFieldKey.[_NewEnum]
then save the ".cls" file, and import it back into your VBA project.
As you can see, both are hacks, but they're accepted ways around the problem