for i =1 to IleDat ' to należy obliczyć lub wstawić stałą
 cells(i,1) = "'" & format( cells(i,1).value,"yyyymm")
next

Option Explicit

Sub KonwersjaDataTekst() ' daty w kolumnie A
 Const F As String = "yyyy-mm"
 Dim lWiersz As Long
 Dim tblDat
 On Error GoTo EXIT_ERR
 Application.ScreenUpdating = False
 'Application.ErrorCheckingOptions.NumberAsText = False
   With ThisWorkbook.Sheets("Arkusz3")
     lWiersz = .Columns("A").Find("*", SearchOrder:=xlRows, _
              SearchDirection:=xlPrevious).Row
     tblDat = .Range("A1:A" & lWiersz).Value
     tblDat = Application.WorksheetFunction.Transpose(tblDat)
     For lWiersz = LBound(tblDat) To UBound(tblDat)
         If IsDate(tblDat(lWiersz)) Then
            tblDat(lWiersz) = Replace(Format(tblDat(lWiersz), F), "-", "")
         End If
     Next lWiersz
      With .Range("A1:A" & UBound(tblDat))
           .Value = Application.Transpose(tblDat)
           .NumberFormat = "@" 'użycie prefiksu "'" powoduje wyświetlenie w formacie daty
      End With
   End With
  Application.ScreenUpdating = True
  Exit Sub
EXIT_ERR:
 Application.ScreenUpdating = True
 MsgBox "BŁĄD : " & Err.Number & vbCrLf _
        & "OPIS : " & Err.Description
End Sub