@quadrica – it depends on whether you mean “in different networks” that you already know about, or different networks, meaning when you first connect to a brand new network that the Pi never knew about. If you have two Wifi Networks (or three) that you already know about and you know their SSIDs and the PSK, you can look to this forum post to see how to set up wpasupplicant to do it (in short, you just add two network blocks in the wpasupplicant config, which you’d need to use in lieu of /etc/network/interfaces probably).
If you’re trying to make it so that new networks pop up on your screen when you go to a new place, you’re probably looking for some sort of desktop UI for wifi kinda like Network Manager, but that requires installation of a full desktop environment for Linux. You could do that, of course. After you install openbox, like I suggested above, check out this post:
Which talks about how to install a Network Management GUI into a Linux desktop UI.
The other alternative is for there to be some sort of Wifi management tool built in to the Zynthian UI, which has been asked about before: