How does lv Montaigne Media become smaller?

How does lv Montaigne medium become smaller? Lumeng Tanaka is a small bag, but its back is very big. You can enlarge the shoulder strap, buy a horseshoe buckle, put it on the ring on the left of Montaigne, tie one end of the shoulder strap on the ring on the right of Montaigne, and tie the other end on the ring on the right through the horseshoe buckle, so that the lv Montaigne will not get smaller.