If you wish to undertake maintenance tasks on your own TGB Express 125 then it is usually recommended to possess a Workshop Manual to use as a reference if perhaps you want to know ways to take out a specific part including Door and match it again properly.
TGB Express 125 Workshop Manuals offers clear specific diagnostic guidelines with regards to your car therefore if something is not working it will help you identify what the situation is and tips to repair it. You can then assess if you can do this on your own or if ever the job is simply too big you can book your Express 125 in to a trusted friendly mechanic.
TGB Express 125 manual