There is an adjuster nut there - but first you need to determine if the slop
is in the steering box or the intermediate shaft.  Have someone grab hold of
the coupler right at the steering box with a big pair of pliers.  Then,
while holding firm, you try and turn the wheel.  If the slop is still there,
it's due to worn U-joints in the steering shaft.  If everything is tight,
then the play is in the box.

If it's the shaft, there's not much you can do but replace it.  If it's the
box, the adjuster nut is located in the center of the sector shaft cover
plate, on the top of the box (opposite the pitman arm).  It's a lock nut
around an allen-head adjuster screw.  Loosen the locknut, tighten the
adjuster screw, then re-tighten the locknut.  Now, you need to be careful
not to apply too much preload via the adjuster - you'll cause even more wear
to the gear.  I wouldn't go any more than 1/4 turn on the adjuster screw.