Find dupicate values within Column

if you want to highlight duplicate values in column then try below code

Sub test()
Dim LR As Long, i As Long
LR = Range("A" & Rows.Count).End(xlUp).Row
For i = LR To 2 Step -1
    If Range("A" & i).Value = Range("A" & i - 1).Value Then Range("A" & i).Font.ColorIndex = 3
Next i
End Sub