Your machine has an "EPA" carburetor. Starting in 1997 The EPA placed requirements on how clean small engines are required to burn. As part of this restriction the carburetors are set at the factory. The carb then either has the adjustment ports capped or they use special adjustment screws so that the carb can only be adjusted by a tech trained in compliance with the EPA directives. The manufacture offers the special carb adjustment tools their authorized repair shops but not to the general public. The manufacture is liable to ensure that the equipment they sell complies with the EPA directive and therefore will typically not offer the adjustment tools for sale to the general public. You can learn more about the EPA emissions requirements for small engines at the following link...
Before you adjust the carburetor you should determine why it needs adjustment first. A carb should only need adjustment when it is new and needs to be adjusted for altitude or after a carburetor rebuild has been performed. If a piece of equipment has been working fine and then starts acting up there will be more repair issues than a simple carb adjustment. The carburetor itself will not simply go out of adjustment. You will want to look at things like a tune up, a clogged carburetor, a plugged exhaust system, ignition problems, etc. Adjusting a carburetor requires some knowledge and experience with small engines. You can easily overheat and seize the engine if you are not familiar with the proper procedures. It is also a good idea to use an engine tachometer to be sure that you make the correct adjustments.
I hope this helps with the repair of your small engine!