can you explain EXACTLY what you need but assuming you mean:

eg Slide 2 Notes page =1
Slide 3 Notes ="FG1"

This should work (make sure numbers are visible before running)

Sub notepage()
    Dim osld As Slide
    Dim oNum As Shape
    Dim x As Long
    For Each osld In ActivePresentation.Slides
        For Each oNum In osld.NotesPage.Shapes
            If oNum.Type = msoPlaceholder Then
                If oNum.PlaceholderFormat.Type = ppPlaceholderSlideNumber Then
                    If osld.SlideIndex / 2 = osld.SlideIndex \ 2 Then 'it's even increment
                      x = x + 1
                        oNum.TextFrame2.TextRange = CStr(x)
                    Else ' it's odd ad "FG"
                        oNum.TextFrame2.TextRange = "FG" & CStr(x)
                    End If
                    'remove slide 1 number
                    If osld.SlideIndex = 1 Then oNum.Delete
                End If
            End If
        Next oNum
    Next osld
End Sub