Braun Hand Blender shaft slides downwards

Hello

I've had this unit for years no problem. This morning my son was using it and the shaft that holds the blades kinda slid downwards, and now when I use it, it always comes down when I blend. I can push it up again but it wont' stay.

I will bet I can fix it, but I don't know how to open up the hand blender. There are no screws, and I don't want to break anything by prying it.

Anita