whether you use a long top or a dress just cut under the armpit. you then have two piece's. the top and the bottom

now with the bottom, this part will be your skirt. turn it inside out, and up at top turn it down about an inch and secure it with pins.

get your sewing machine and start sewing. to remind you when sewing, your bottom part of the long top/ dress should still be turned inside out.

thats it. three simple steps and you have your own bodycon skirt, using a long top or dress.
Enjoy :D