1. Hot water soaking method: soak the sweater in hot water of about 70 degrees, take it out about an hour later, then soak it in cold water until the water temperature becomes cold, finally take out the sweater, squeeze it out gently, don't rub it hard, and then dry it flat.

2. Steam iron: Ironing a sweater with a steam iron can soften the fiber and restore it to its original state. Be careful that the temperature of the iron is not too high to avoid scalding the sweater.

3. Hot water bath method: when taking a bath, hang the sweater on the bathroom door, soften the clothes fiber with steam, and then restore to its original state.

4. Cold water bath method: soak the sweater in cold water for a few minutes, gently squeeze out the water, and then lay flat to dry. This method is suitable for thin knitwear.

5. Cutting method: If the sweater becomes loose, you can find a professional tailor to cut it locally to restore the sweater to its original state.

Among the above methods, hot water soaking method and steam iron method are relatively simple, easy to operate and suitable for home operation. However, it should be noted that some methods may not be applicable due to the different materials of sweaters. Before use, it is recommended to check the material description of the sweater.