To adjust the steering play, you need to adjust the allen key in the centre of the steering box.
Firstly, mark both the allen key and the securing nut (in the same place so that you have a starting reference point).
Holding the allen key firmly, release the securing nut and turn the allen key a quarter of a turn clockwise. Resecure the locking not whilst holding the allen key firmly.
You need to lift the front wheels off the ground to check that the steering isn't binding.
With the engine running, turn the steering from lock to lock, if it won't go full travel both ways, then you need to slacken off the allen key and adjust a fraction anti-clockwise....., it's a trial and error adjustment.
If it does travel fully without binding/locking, then take it for a low speed road test doing full lock three point turns just to make sure that it doesn't lock under weight.
Chris