Hi, and welcome to the iFly family!
Open iFly, navigate to the Lax Vor on the VFR map. Place a finger over the Vor, and place your adjacent finger on the 123 radial a distance away. The distance between the two points wii be displayed, and be adjusted to fine tune to 17 miles. Once you get the distance where you want it, press anywhere to remove the distance bar, then press and hold the spot that was 17 miles from the Vor. Use the pop-up menu to create and save a custom way point.
Hope this helps.