Handlebar re-alignment
As abdnChap says rotating the stem around the steerer tube can be accomplished by loosening the stem bolts.
However, you may need to re-adjust the headset bearing pre-load if you loosen the stem bolts, and the pre-load may not have been set properly when the bike was assembled.
To pre-load the bearings the bolt in the top-cap is tightened to pull the fork upwards slightly before the stem bolts are fully tightened. There should be no play of the fork or bars in the head tube, but the bars should turn freely. You can check for play by applying the front brake, holding the bars and rocking the bike backwards and forwards.
This Park Tool video shows how to install a stem and includes alignment and setting bearing pre-load. The pre-load adjustment procedure starts at about this point.