How to "open" the game, get the data?

Question

Lua

One old toy has long been closed, I don’t know the exact information on what it was written on.
In the elements you can find the code in lua (there seems to be most of it).
And, as far as I remember, the lua coders found the last game files before the project was closed, opened them, slightly changed them, and even brought their servers there.
*I understand that the question may not be professionally asked, but I'm trying to understand how it works, because the game was not able to rework at all.