da codice potresti fare una cosa cosi

Private Sub Command1_Click()
Dim a As String
Dim b As String
Dim c As String
Dim d As String

a = "mm/gg/aaaa"
b = Left(a, 2)
c = Right(a, 7)
d = Left(c, 2)
a = d & "/" & b & "/" & Right(a, 4)

Text1.Text = a
End Sub

ciao