Sub test()
Dim DateATester As Date
Dim Mois As String
DateATester = Sheets("Feuil1").Cells(1, 1)
Select Case Month(DateATester)
Case 1
Mois = "Janvier"
Case 2
Mois = "Février"
Case 3
Mois = "Mars"
End Select
If Day(DateATester) = 1 Then
Sheets("Feuil1").Cells(2, 1) = "1er " & Mois & " " & Year(DateATester)
End If
End Sub