The commented out lines are the lines I used to create the table. You don't
need them because, of course, the table already exists in your database ...

Public Sub AddIndex()

   Dim db As DAO.Database
   Dim tdf As DAO.TableDef
   Dim fld As DAO.Field
   Dim idx As DAO.Index

   Set db = CurrentDb
   'Set tdf = db.CreateTableDef("tmpTable")
   Set tdf = db.TableDefs("tmpTable")
   'Set fld = tdf.CreateField("Approved", dbBoolean)
   'tdf.Fields.Append fld
   'db.TableDefs.Append tdf
   Set idx = tdf.CreateIndex("Approved")
   Set fld = idx.CreateField("Approved", dbBoolean)
   idx.Fields.Append fld
   tdf.Indexes.Append idx

End Sub