Sub test()
Set c = Range("I2:K" & Range("I" & Rows.Count).End(xlUp).Row)
For Each cel In c
If IsDate(cel) Then
If cel.NumberFormat = "d-mmm" Then cel.NumberFormat = "dd-mm"
If cel.NumberFormat = "mmm-yy" Then cel.NumberFormat = "mm-yy"
End If
Next
End Sub