Familiar with Distagon Hasselblad 3.5/60mm?

Well, here's my problem...
I recently bought a Distagon 3.5/60mm lens to use on a Nikon D800. I'll be using it with a Mirex adapter. My problem is with the lens. There are two issues I need to resolve (one in this post) and fairly quickly as I intended to travel overseas soon with this combination. The lens has a screw release on the rear of the lens that, when turned in the direction of the bright orange arrow above it, closes the aperture blades. Of course I can't take photos like that but I don't know how to reverse the problem. Is it a simple solution? Hoping...