If the bell crank has been removed, or you just want to check the adjustment, screw it all the way onto the axle, then back it off to align towards the cable. Then, tighten the lock nut. then adjust the cable with the shifter in the 2nd position to put the N in the center of the window. Then, when you are in 3rd, there should be no tension on the cable. When in 1st, the cable should not be able to be pulled out any more.

I broke a bell crank once and I was able to keep the bike going until I got a new one by using a metal rod and an acorn nut to hold the hub in a lower gear.