The lever to open it is that thing on the front, left side. It is hinged on the bottom, so you need to pull on the pointy end. There isn’t anything special about it so not sure how it’s jammed on your camera. It seems pretty robust too. It doesn’t need much force on my camera, but it feels like it’s unlikely to break if you pull a bit harder.

Once that is open (pointing towards the front of the camera), the whole backside+bottom just drops out.

That probably didn’t help much, but I can’t think of a better way to describe it 🙂