Spread the sweater flat, cover it with a semi-wet towel, and iron it slowly with an iron. If you don't have an iron, you can find an enamel cup or an aluminum lunch box, and then fill it with boiling water (not too much water, too much water is easy to overflow) to iron the sweater slowly, and the effect is good. If it is a sweater that has just been knitted, just wash it directly. Because the newly knitted sweater may have a little uneven stitches, it will naturally walk evenly and look flat after washing. There is also steaming in a steamer and then drying.