The piece in the middle of the shroud with a notch towards the bolt body is what I would call the cocking piece; the notch is the sear notch which holds the striker cocked until the trigger is pulled. IME, you need to pull that piece back against the striker spring pressure, then rotate the shroud.
I don't have this model, but when I do this with other similar rifles, I use something like a chopstick, hook it under the sear notch, and use that to pull the cocking piece back while rotating. I've also done it by pushing the bolt down against the edge of a bench while catching the sear notch on the bench. I wouldn't use anything steel for fear of damaging the surface interacting with the sear.
A careful look at the cocking ramp should tell you which way to turn. You probably can't just hook the striker with a finger and recock it. Once you've located the sear and determined which way it should rotate, use the edge of a 2x4 or such so you don't burr the striker surface.