Step 1, wet the neckline, put it into the shape you want, iron it, and dry the bungalow;

Step 2: T-shirt neckline has welt. You cut a little from the inside, put on a thin elastic band (elastic band can be bought and changed in a cloth shop or a tailor's shop) and go in. The length of the elastic band should be just right. Don't pull up the neckline and sew the elastic joint to death. Just sew the cut back with a thin thread, cotton won't come off easily.

The elastic band can be inserted with the simplest black clip. If the boy doesn't have a hairpin, use a paper clip to straighten it from the middle, keep both ends bent, and bend the leading one to death, so that the elastic band can be inserted into the clothes.