If you have a J-M series snowcasters, the auger mounting plate has many holes in it and can be positioned around many different orientations.
The hex pin on the bearing plate is slightly eccentric ... as you rotate it, the auger moves slightly inward or outward to the housing. This takes up slack in the chain.
Newer models have the adjuster on the driveshaft end of the chain.
Generally it is considered best to start off with a fresh chain, as clearance between the auger and housing will degrade performance of the snowcaster. A fresh chain is the best position available.
Good luck with it ...