There is a functional belt also made from flexible filaments that was designed for this skirt and it will be released shortly after this one. A skirt for barbie sized dolls. Printed in flexible material. A heating impliment is required, suchs a lighter or heatgun( which means be careful and if you are not an adult then *adult assistance and supervision is required*. I would insist that you take precaution and work in a safe environment while using open flame, especially.
Simply heat each flap section at the point of insection with the body of the skirt. Be careful to apply just a couple of seconds of heat til the material softens then bend the intersection to make the flap more parallel with the body of the skirt. Repeat.
This object was made in Tinkercad. https://www.tinkercad.com/things/6mi9rja5cOC