There are some ideas for you
1. Soak the shrunken sweater in warm water with fabric softener, then leave it for an hour until the fibers soften, then slowly pull the sweater back to its original shape, and finally lay it out to dry.
2. Use an iron to heat the sweater (Check the label on the sweater first to prevent demage the sweater), or heat the sweater in a steamer for 10-15 minutes and stretch the fibers while still hot to restore the sweater to its original shape (using an iron to heat the sweater requires multiple reheating).
3. The third method is to find a thick cardboard, cut the cardboard into the original size and shape of the clothes, the edge of the thick cardboard is suggested to use some tape to wrap to prevent damage to the sweater, put the sweater into the cardboard, use an iron to heat repeatedly, and then wait for the sweater to cool down.
