Too "soft" as in too much power assist? That's standard for the earlier Jeeps, unfortunately. There is no adjustment for that, it's a function of the spool valve in the steering box. It can be changed out for a spool valve from something like a performance package Camaro or Firebird, but now you're talking a lot of work.
If you mean a bit too much slop or free play when going straight ahead, there is an adjustment screw in the top of the steering box. Look closely and you'll see a cover plate with three hold-down screws, and a fourth screw in the center with a slot in it, and a locknut. That's the over-center adjuster. To adjust, back off the lock nut and tighten the screw, then lock down the locknut again.
CAUTION: Over-tightening this screw will ruin the steering box. First, this adjustment MUST be made with the steering gear in the straight ahead position. Second, do not over-tighten. These are recirculating ball steering boxes, not rackety pinion, and you will not/cannot get it to feel as precise as rack & pinion steering.
Also, with a '91 don't overlook the very likely probability that some of your steering looseness may be due to worn/sloppy tie rod ends, ball joints, and/or track bar. Eliminate other potential causes before attacking the steering box.