Screw that I'm sure it's a stock swing arm and bearing carrier.
There is two long bolts on your bearing carrier (part that your axle slides through). Loosen both of those just a tad and rotate the bearing carrier backwards toward you. This will tighten your chain up. If your bearing carrier is hard to rotate or move back and forth for chain adjustment, use a pry bar of some sort for motivation to free it up.
Once you get your chain tightened to your liking, tighten the two bolts back that you loosened when you started. Chain should have a little slack in it, you don't want it super tight.
If you max out the adjustment on the bearing carrier, find the master link on your chain, take the chain off and remove a link or two from your chain, then re-install.
Problem solved.