Which platform can I find to change the lock? About how much will it cost?

You can find the master of unlocking and changing locks in 58 cities, usually around 50- 100.

Lock core:

The lock core adopts a number of anti-theft technologies and a variety of special-shaped anti-pulling marbles to prevent the technology from opening. Unique marble and blade design has high safety performance for technical opening. The lock core is equipped with accurate numbered marbles and special-shaped marbles. When the numbered marbles and special-shaped marbles must be pulled at the same time when the technology is opened, it will automatically lock, which makes the technology opening fail. The lock core adopts multiple combinations of various special-shaped marbles, and at most one billion key numbers can be compiled to realize zero mutual opening in the area (11 in 6 million).