Hi

Try this code.

Code:
Private Sub Worksheet_Change(ByVal Target As Range)
     
    Dim rFound As Excel.Range
    Dim rCount  As Long
    
    
    If Target.Column = 2 Then
        
        rCount = Application.WorksheetFunction.CountIf(Me.UsedRange.Columns(2), Target.Value)
        
        If rCount > 1 Then
            Set rFound = Range("B:B").Find(What:=Target.Value, MatchCase:=False, Lookat:=xlWhole)
             
            If Not rFound Is Nothing Then
                
                If MsgBox("The registration Number  " & Target.Value & _
                "    has been found in row  " & rFound.Row & vbCrLf & vbCrLf & _
                "Do you want to view this entry?", vbQuestion + vbYesNo, "Confirm") = vbYes Then
                     
                     '// You might want to delete the 'new' entry/entire line here
                     '// otherwise the suplicate remains.
                     '// Application.EnableEvents = False
                     '// Target.Value = vbNullString
                     '// Application.EnableEvents = True
                     
                     '// Application.Goto rFound, True
                    rFound.Activate
                End If
            End If
        End If
    End If
     
End Sub