It's been 15 years or more since I saw one of these and my memory isn't what it was... but if the S was the version with the 40/2.8 Sonnar I think I remember that the front bezel is removed and behind it is a clamping ring with (3?) small screws - loosen screws, adjust infinity setting, tighten screws.
A focus screen on the film rails can be used to determine infinity focus of the lens, in this position move focus ring to inf. stop & tighten clamp.
I'm fairly sure some models of the 35 did have a tiny grub screw or 3 in the edge of the focus ring though to lock it to the lens.
I can't remember whether the bezel is screwed in or not but I don't think so.
It may have clicked into place with barb-locks or have been fixed with adhesive, or both.
Sorry I can't offer any real advice on this one... except to say it's a very nice lens and I would send it to a Rollei repairer rather than risk DIY - it shouldn't cost much if this is the only fault.