"Go back" in what?
If you're reading, just swipe from right to left.
If you want to "go back" to whatever you were previously doing, use "backswipe." There is a sweetspot on the status bar (the one with your time and battery on it.) Turn your wi-fi on. Just to the left of the wi-fi symbol is the sweet-spot --- swipe from right to left (thumb flick it) and it will "go back."
