If you wish to conduct maintenance on your own Honda CRF50F then it is always recommended to have a Workshop Manual to use as personal reference should you need to know proven methods to take off a certain component such as the Gearbox and match it again in the correct way.
Honda CRF50F Workshop Manuals are able to offer particular diagnostic guides for the vehicle so if something is wrong it can help you ascertain what the issue is and the best way to repair it. You can then determine if this can be done on your own or that the job is too big you could make a booking for your CRF50F in with a local garage.
Honda CRF50F manual