Normally the Trek dealers offer a free tune up within the first year. Gives them a chance to check over the bike. They should also be willing to lower the bars.

If you have the tools, allen wrenches and torque wrench you could just remove the top cap and loosen the stem. Then move some spacers on top of the stem. Do this and ride a bit to check the bar height is to your liking. Then later unless you have the tools, ask the shop to shorten the steerer tube. You can shorten it but cannot lengthen it. Well you can but that requires a new fork. Enjoy your new ride.