If you want to do repairs to your Veli VL125GY 2 then it is usually recommended to have a Workshop Manual for a guide if you need to know the way to take off a certain part much like the Brake Discs and install it again appropriately.
Veli VL125GY 2 Workshop Manuals will give you distinct diagnostic info on your vehicle therefore if something is wrong it can help you determine what the issue is and how you can fix it. You will be able to decide if you can do this by yourself or in case the job is just too big you can book your VL125GY 2 right into a decent mechanic.
Veli VL125GY 2 manual