FAI Triangles are considered Formula 1 in Cross Country soaring for many. You may be triangle specialist or novice. You will always need help with defining FAI triangle waypoints.
There is no easy way to plan an FAI Triangle. It takes time and preparation. Mountain ranges will have to be crossed and airspace avoided. Lots of terrain will be covered with many different types of weather. Thorough local and weather knowledge is required to plan for the largest of triangles. SeeYou tries to make flight planning as easy as possible.
First you need to create a task that roughly resembles what you are going to fly. Define your waypoints by clicking on them in Map view or entering them manually in List view (see How to planning a badge and record flight ? for more on this subject). Then switch to View > Map mode.
Turn the FAI Triangle Assistant on by selecting View > Show FAI Area (Ctrl + E). Press Ctrl+R (View > Rotate FAI Area) to Rotate the Area over Task legs. Press Ctrl+R several times to see what it is doing. Once you have it located over the turnpoint you are trying to optimize, stop pressing Ctrl+R. Click on the Waypoint and drag it into place. When it is inside the FAI Area, the Task has a shape of an FAI Triangle.
As noted above - there is no quick way to create an optimum FAI Triangle. You have the tools, now you need to use your imagination and experience to minimize the difficulty of rounding the Turnpoints.