If your chain needs to be adjusted, the first thing you need to do is crack the axle nut loose. Don’t spin it off, just loosen it enough to allow the wheel to move in the swingarm. There are several different styles of axle adjusters out there, but most will have a lock nut that you need to crack free. Then turn the adjuster ¼ turn at a time to shift the axle position and change the chain slack. Make sure you’re moving the left and right side the same amount, and check the reference marks on the adjuster to verify that the wheel is straight in the swingarm.