If you want to conduct auto repairs to your CZ 125 then it is usually a good plan to have access to a Workshop Manual to keep just for reference in the event you want to know proven methods to remove a particular part including Gearbox and fit it again safely.
CZ 125 Workshop Manuals will give you certain diagnostic information for your car or truck so if something is playing up it helps you find out what the issue is and the way to make it better. You will be able to assess if you can do this by yourself or if ever the job is just too big you could make a booking for your 125 into a trusted car garage.
CZ 125 manual