Connect to a previously used Wi-Fi network
Your device automatically connects to known networks, so you don't usually have to do anything. Turn on Wi-Fi if it is off (learn how).
To use a different known network: Open Wi-Fi > tap the network name.
To stop your device from joining a known network by itself: Open Wi-Fi > touch and hold the network name > turn off Connect automatically > Done.
Checked against the LuneOS code and installed apps. Nobody has tried these steps by hand yet, so tell us if something differs.