Code works to :
List all unique values from column A in Column B, starting with row
12.

I need to know how to change the criteria in the code to do the
following:

List all unique values from column L, in column Q, starting with row
12.

(I tried changing the obvious letters.... but must be a little more to
it!).

Private Sub Worksheet_Change(ByVal Target As Range)
Dim myRow As Long
If Target.Cells.Count > 1 Then Exit Sub
If Target.Column <> 1 Then Exit Sub
Application.EnableEvents = False
If Application.CountIf(Range("B:B"), Target.Value) = 0 Then
  rw = Range("B65536").End(xlUp)(2).Row
  If rw < 12 Then rw = 12
  Cells(rw, 2).Value = Target.Value
End If
For myRow = Range("B65536").End(xlUp).Row To 12 Step -1
  If IsError(Application.Match(Cells(myRow, 2).Value, Range("A:A"),
False)) Then
      Cells(myRow, 2).ClearContents
  End If
Next myRow
Application.EnableEvents = True
End Sub