There's two ways to forward or rewind:
With the progress bar
Put your finger on the progress bar and swipe left or right to go to an earlier or later point in the book. You can always undo this is if you have moved to the wrong place.
With the forward and rewind buttons
With the buttons that you find on either side of the play button you can move forward or backwards in your book. The standard time interval for these buttons is 15 seconds forward or back but if you press and hold them, you can change the time interval to up to 30 minutes. You can also change this by clicking on the gear symbol above the book cover.