Pull the right front side cover, like you were going to check the oil. You will see the bellcrank that has two cables connected to it. That's the adjustment end for the reverse lever. Put the lever into the reverse position, you'll see a little - mark on the right end of the bellcrank, it should line up with a little fingerlike pointer molded into the engine case. On the left end of the bellcrank is another - mark. with the lever up, there should be 1/16"-1/8" free play. When you adjust the cables, put the bike on the side stand in neutral. Pull the reverse lever up and check that it's in reverse by trying to turn the rear wheel.
When adjusting the cables use the left hand adjusting nut on the left hand cable to align the right hand index on the bellcrank. Use the right hand adjusting nut to set the free play on the left hand index mark. It's done this way because the lever pulls the left hand cable to go into reverse. So that's the cable that needs to adjust the amount of bellcrank travel. The other cable just determines the amount of free play so that the system won't bind.