Awww, I am so sorry about this. It looks like a total blister! Was the leather wet or dry when you took this pic?
Try drying it for couple of days and see how it goes
If it hasn't improved by now, you could ask Docride on the Hermes Vintage Bag Nightmares & Hermes Leather Care on how you may be able to treat/minimize it. I'd suggest do it sooner rather than later. G'luck!