Sub Convertir()
Dim t, i&, x$
If ActiveSheet.FilterMode Then ActiveSheet.ShowAllData 'si la feuille est filtrée
With Range("D1", Range("D" & Rows.Count).End(xlUp)(2)) 'au moins 2 éléments
t = .Value 'matrice, plus rapide
For i = 1 To UBound(t) - 1
x = Format(t(i, 1), "00\/00\/00")
If Not IsDate(t(i, 1)) And IsDate(x) Then t(i, 1) = CDate(x)
Next
.NumberFormat = "dd/mm/yyyy"
.Value = t
End With
End Sub