Hi I am not a trained mechanic and I am sure that someone with a better knowledge may help but it sounds to me like the adjuster hub is possibly seized quite common if not maintained they are supposed to be greased every so often with the suspension linkages. I forget the timescale, but a search here on the forums should point you in the right direction and it will be listed in the maintenance schedules. Hope you get it sorted.
All you need to do is loosen the clamp bolt. Try a little penetrating oil. I know the early 1050's like my '06 prefer the chain on the looser side of the spec, I think the 955's are the same. Too tight will wear the chain and bearings quickly.