The reeds are still sealed in beeswax. It is the wooden box that holds the three reeds that has come loose, exposing the sound hole. It looks like some type of clear glue was used previously. Is that beeswax also? The beeswax around the reeds looks a dark brownish reddish color.
Ah, the pics cleared up my misunderstanding. It is the reed blocks that came loose. Any wood glue will work. Make sure to press firmly so there is good contact and no gaps that air can get through.