Code need to be expanded and running faster

Do not hard coded range, instead use count.

Option Explicit

Sub DDMMYYSpain()
Dim ws As Worksheet
Dim rCell As Range
Dim rng As Range
Set ws = Sheets("spain")
Set rng = ws.Range("K2:K" & Range("K" & Rows.Count).End(xlUp).Row)
For Each rCell In rng
    If Len(rCell) Then
      rCell.NumberFormat = "@"
      rCell.Value = Format(rCell.Value, "DDMMYY")
    End If
Next rCell
End Sub