Using the full pad of your thumb and slow and very deliberate on touching or scrolling the screen. See the pictures of where the sensors are and the picture of the screen without the glass. Pausing a beat when touching or scrolling is advised.

You can see in this picture where the screen buttons are. You will want to index your fingers towards the points of the up and down arrow. The down arrow is sometimes difficult to reach and you may have to press down on the cup tray slightly.