How to create or customize your own board

[Dabittosan]

Hi I just bought the base game and I am loving it. I've been playing Catan for a very long time and a big part of the game is creating the map.

Maybe I'm a bit confused but I can't find an option to create my own custom board and that would seem like a pretty important feature in order to recreate the experience of the physical board game.

Having played so many times, my friends and I like to create special boards where each sides are mirrors of each other for example. Maybe these custom maps could only be played in a private friendly match and not online with strangers or something, but it would be nice to have.