Move cursor to start of masked field. Set as On Click event.

MoveFirst.vb

Sub MoveFirst()

  Dim acform As String
  Dim accontrol As String
  
  acform = Screen.ActiveForm.Name
  accontrol = Screen.ActiveControl.Name
  
  Forms(acform).Controls(accontrol).SetFocus
  Forms(acform).Controls(accontrol).SelStart = 0

End Sub