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It is difficult to find because it isn't there... Map Pilot Pro does all flight layouts in the app itself.
If you want to define the area you want to cover using a desktop you can either layout a polygon using Google Earth and import it into Map Pilot Pro as a KML or you can define a boundary on the Maps Made Easy site and sync it with Map Pilot Pro.
https://support.dronesmadeeasy.com/hc/en-us/articles/360029963631-How-to-create-Boundaries