In the past, WiFi connection problems were related to an incorrect date, time, and time zone selected, so you might want to check that in the Settings app. If it’s wrong, you might have to disable automatic and then set them manually (the first time). After that you can revert to automatic.
If that’s not the problem, and you’re sure the kill switches are not engaged, you might try flicking them the opposite direction, waiting a half minute or so, then flicking them back. (When they’re all in the “up” position, i.e. toward the top of the phone, then they’re not blocking any circuit.)