Touch down on the scrub pad (see arrow below) and move left and right of center to make minor adjustments to your rider position within the lap. The closer to center the slower the adjustments, and the further from center the faster the rider will move. This is a great tool for moving one data point at a time, especially if you are using the extra data views (graph display of your data and want to look at specific data points, like peak speed, etc).
You can use the slider at the very bottom of this screen to make large adjustments, like quickly jumping to the end or beginning of your lap.