How to open .dat files?

[LiveseyY]

Good afternoon! I know this is a stupid question, but....
I'm creating a mod about the Russian Civil War of 1918-1922 and I want to edit some of the game's parameters, in particular: possible dates and the location of railways on the map. I did not find the necessary functionality in the editor and concluded that it could be edited in the GenData files, but I could not open them, no matter how hard I tried. I would be very grateful if someone would explain to me how to do this and if it is even possible. Thanks! (I'm sorry, I do not speak English, the translation was done over the Internet.)