This should be a pin or hole change lock. The advantages is you do not need an extra change key. The disadvantage is you need to disassemble the lock.
The combo change of a mesh change lock is shown here:
https://www.youtube.com/watch?v=x6L_jQJRQXQ The pin/hole change lock is similar, but a bit different. If you are a mechanically interested person, that I guess you will manage. Otherwise I do recommend a safe tech to do this for you. You can probably find one nearby on
http://www.savta.org/ .
If you do anything yourself: Do test the combo at least three times before closing the door.
