What kind of tools do you have?
centershot tool?
nock height tool?

Did you take any measurements when you first got the bow? Was the bow new? String new?
Do you have access to a bow press? If the string stretched , you can put it in a bow press to relax the limbs and twist the string to return it to the proper position.
It depends on where your arrow is sitting on the shelf wether or not I would move the rest or the nock (if it is a tuning issue). I'm guessing you probably do have string stretch which means you need to put a few twists in the string to return it to the proper place.
Did you take tiller measurements when you first got it?