Excel Macro search and copy function in subfolders

Hello everybody,
i've again some problems with my VBA-Code and hopefully some of you can help me.
The macro search in a directory after excel files with certain names and then copy the data to another workbook, this works perfect thanks to the hepf of this forum!
But know, i want that the macro not only copy the data from this folder but als from the subfolders and i struggle to realize that.
I'm really a newbie in VBA, so if anyone could help me with this, that would be great!

Here's my code:

Sub Suchenundkopieren()

Dim directory As String, fileName As String, sheet As Worksheet
Application.ScreenUpdating = False

directory = "C:\Users\YL\Desktop\Test\*"
fileName = Dir(directory & "Quell*.xl*")

Tabelle1.Cells.Clear


    Do While fileName <> ""

    Dim src As Workbook
    Dim lr As Long 'Quelle
    Dim lrZiel As Long 'Ziel
    Dim WsZiel As Worksheet

        Set WsZiel = ThisWorkbook.Worksheets("Tabelle1")

        Set src = Workbooks.Open(directory & fileName, Password:="1234")

        lr = src.Worksheets("Overview").Range("A" & src.Worksheets("Overview").Rows.Count).End(xlUp).Row

        lrZiel = WsZiel.Cells(WsZiel.Rows.Count, 1).End(xlUp).Row
        If lrZiel <> 1 Then lrZiel = lrZiel + 2

        src.Worksheets("Overview").Range("A1:MV" & lr).Copy Destination:=WsZiel.Cells(lrZiel, 1)

    src.Close False

    Set src = Nothing
    Set WsZiel = Nothing

    fileName = Dir

    Loop

Application.ScreenUpdating = True

End Sub

Greetings