Draw images of the wing shape on paper. They should all be to scale, so have a ruler handy. You will want one view from above, one from the front and one from the back.
Place the sheets on the block and use the Sharpie to trace the drawings onto the block. Plug in your hot-wire cutter and let it heat up.
Use the hot-wire cutter to start trimming away pieces of foam. This is very much a sculpting process. While you are trying to reach the lines you drew, remember that shape of the top of the wing between these lines needs to have curved rather than flat surfaces.
Spray paint the wing in the color of your choice to make it smooth.