Shut down the phone and start it up again. On the Welcome screen, use the 4-corner bypass. Tap the upper-left corner below the status bar, then upper-right the same way, lower-right but actually somewhat to the left going closer to the emergency call button, then lower-left similar to the previous one. After you've done this, you can continue with setting up the phone then fix the problem once you are past the setup screens.
If it doesn't work for you the first time, just keep trying until you figure out the locations to tap. Once you figure it out, it should be easy to do it any future times that you need it.