1. Preparation materials: a vest, scissors, needle and thread that is no longer used.
2. Lay the vest flat on a flat surface to ensure that the front and back are aligned.
3. Cut the hem of the vest shorter with scissors. This will become the waist of underwear.
4, on both sides of the vest, starting from the hem, cut two curved trouser legs. You can decide the length and shape of your trouser legs according to your preferences and comfort.
5. Sew the edges of the two trouser legs together with a needle and thread on the inside of the trouser legs. Make sure the seams are firm to prevent the pants from breaking.
6. Above the waist, fold and sew the edge of the vest with sewing needle and thread to form a comfortable waist. You can add elastic bands or ropes as needed to adjust the waist tightness.
7. Check whether your changes are in line with expectations, and make fine-tuning and trimming if necessary.