The screw is tapered and works on a rod that runs the length of the shock shaft and controls oil flow/damping.
The lower hoof of the shock is removeable but the screw is captive so I can't readily be accessed/repaired. As luck would have it, I 'may' have the lower hoof complete with screw in my vstrom box of bits - you are welcome to it for cost of post .- it will need to be accurately measured before & after disassembly otherwise the base damping settings will be wrong.
Phil