There are ways to wipe firmware and yanking the battery for a few minutes is a good way to wipe the birthday, time, favourite monkey.... options but wifi is a bit more difficult (you have to run a game).
head on into to a wifi game (on cart or original).
go into the setup wifi options
Attached to each of the three settings panels is a clear settings option.
Redo the settings as you need.
Before doing that if you just changed your router settings change them back.