How to change the combination of a double bit lock?
The first thing is to remove the door lock and its respective screws. Then remove the cap carefully to prevent the springs from jumping around. Identify where the key is entered and you will find the plates and the latch.
Here you must carefully remove the first two plates, then comes the latch and then two other plates that go underneath. Put them in the reverse order you took them out to re-enter them.
At this point the lock is disarmed. To change the combination, start with the fourth plate you took and end with the first. There you will have your new lock.
How to create the new key?
This is the most complex step. Place both keys with the mark facing up, join them with the press and make their respective marks where you will remove the material. Do this on both sides of the wrench and take a good look at how deep you want to remove the material.
Use a walrus, a saw, and some files to trace over these marks until you reach the desired point. Then test it to see how much material remains to be removed and chalk the excess. Repeat the process until you can turn the lock.