For a modest subscription, you would have access to lists that give you the location of the second number (BDM-Untergau 742) and the matching sleeve triangle. The first number (Mädelgruppe 2), is not yet known to us but there is an ongoing HJ-Wiki project (also part of the Full Member subscriber section) that aims to identify the units directly below Bann/Jungbann/Untergau/JM-Untergau within the organisational structure.
Having said all of that, the general area where this pennant would have been used until 1944/5 is now a part of France and is known as Département Haut-Rhin.
Are you able to post more pictures of this pennant?
Yes more pictures are required to see the stitching of the Untergau/Mädelgruppe numbers and the clips and general appearance. It looks okay on that picture so far