The coverline (the line drawn horizontally across your chart once ovulation is detected) is a visual tool to help you easily see your pre- and post-ovulation temperatures. It has no physiological significance whatsoever so where it is placed does not have much importance as long as it helps you to see your ovulation pattern.
Fertility Friend sets a reasonable coverline based on the pattern of your unique chart.
If the coverline is not where you expected to find it, you may be thinking of the Fertility Awareness Method Rules which place the coverline at one tenth of a degree higher than the 6 previous temperatures before ovulation. If this is the method you wish to use, (it is best suited to those with clear chart patterns), you can use it by adjusting the detector tuning section in the Fertility Friend app. The coverline on the advanced (recommended) setting will usually be found a bit lower to avoid unnecessary anxiety during the luteal phase and to recognize more complex ovulation patterns.