Selecting multiple items from a dropdown list and returning different values

Find attached and the code below as well.

Private Sub Worksheet_Change(ByVal Target As Range)

    Dim Oldvalue As String
    Dim Newvalue As String
    Dim selectedNum As Variant
    Application.EnableEvents = True
    On Error GoTo Exitsub
    If Target.Column = 3 Then
        If Target.SpecialCells(xlCellTypeAllValidation) Is Nothing Then
            GoTo Exitsub
        Else: If Target.Value = "" Then GoTo Exitsub Else
            Application.EnableEvents = False
                     
            
            Newvalue = Target.Value
            selectedNum = Application.VLookup(Newvalue, ActiveSheet.Range("dropdown"), 2, False)
            Newvalue = selectedNum
            Application.Undo
            Oldvalue = Target.Value
            If Oldvalue = "" Then
                Target.Value = Newvalue
            Else
                If InStr(1, Oldvalue, Newvalue) = 0 Then
                    Target.Value = Oldvalue & ", " & Newvalue
                Else:
                    Target.Value = Oldvalue
                End If
            End If
        End If
    End If
    Application.EnableEvents = True
Exitsub:
    Application.EnableEvents = True
End Sub

DDBDS