If you wish to conduct maintenance tasks for your Honda TRX400X then it is usually recommended to possess a Workshop Manual to use as a reference in the event you want to know methods to strip off a specific component for instance the Gearbox and install it again the right way.
Honda TRX400X Workshop Manuals can provide exact diagnostic guides on your vehicle therefore if something is broken it helps you figure out what the issue is and how you can repair it. You will be able to analyse if you can do this by yourself or in the event the job is just too big you are able to make a reservation for your TRX400X in with a decent garage.
Honda TRX400X manual