Somebody has turned the bolt shroud 90deg anti-clockwise, uncocking it. That's easy to do.

It's a bit harder to turn it back in its cocked position, but not really difficult.

When you look at what is the bottom of the shroud, you see the rectangular protrusion of the cocking piece. Its nose is engaged at the bottom of a V notch in the rear of the bolt body. This piece needs to rotate clockwise with the shroud, climbing the ramp on the notch, and it will click in its cocked position, which is a tiny notch on the back of the bolt body.

If your bolt is not too rough, simply holding the shroud tight and turning forcefully clockwise should do the trick. Wrapping it in a rag may help.

If it's too hard, one way is to use the corner of a wooden table (one on which you don't mine a scratch or dent, which is a possibility...) You hold the bolt vertically, firing pin end down, and catch the cocking piece on the wood. You can then press the bolt down, at the same time rotating the shroud.