This is just based around what is on my 36. The chain has a screw adjuster unit as part of it. You need to have the rudder right over (can't remember which way) to access it (on mine) through an inspection cover in the pedastool. Thing is, if the chain you have was the correct length (in no of links) when it was fitted and adjusted up correctly and you now have 2" + of play, you may need a replacement. If you need to take some links out to tighten it, then such a badly worn chain made tight again to fit, will wear out your sprockets as the pitch will be wrong. If you do have an adjuster, maybe it has just come loose, so that is worth checking. If your sprockets are still good (not hooked or damaged, then it maybe worth taking the chain off and checking wear in the rollers.
Alternatively, if there if defo no adjusters anywhere, then there will probably be a split-link somewhere on the chain.
Apols if I its sounds like I am teaching Granny etc!!