Не проверено, но для этого нужно:
Option Explicit
Sub Overlap()
Dim wb As Workbook
Dim ws As Worksheet
Dim LastRow As Long, LastCol As Long
Dim rng As Range, Rng2 As Range
Dim Cell As Variant, Double As Variant
Set wb = ThisWorkbook
Set ws = wb.Worksheets("Whatever")
LastRow = ws.Cells(wsV.Rows.Count, "A").End(xlUp).row
Lastcol = ws.Cells(1, .Columns.Count).End(xlToLeft).Column
'Your entire range, here in column A
Rng = ws.Range(ws.Cells(1, 1), ws.Cells(LastRow, LastCol))
' Loop through each cell of the Range
For Each Cell in Rng
'Set a new range, from the beginning of the orginal one to your current row
Set Rng2 = ws.Range(ws.Cells(1,1), ws.Cells(Cell.Row,1))
With Rng2
Set Double = .Find(Cell.Value, LookIn:=xlValues, Lookat:=xlWhole)
' If double is not nothing you've found the value of the current cell
' Meaning there's more than one
If Not Double Is Nothing Then
'Here you found a duplicate value - Do what you need to do
End If
End With
Next Cell
End Sub