If you have to accomplish adjustments on your Yamaha YZF R6 then it is usually a good plan to possess a Workshop Manual to use as a reference if you need to know ways to remove a particular part including Gearbox and match it again correctly.
Yamaha YZF R6 Workshop Manuals can offer you specific diagnostic guides on your car therefore if something is broken it will help you find out what the issue is and tips to repair it. After that you can assess if you can do this yourself or if the job is too big you can still book your YZF R6 in with a suitable car garage.
Yamaha YZF R6 manual