Ran across this; I did not know!
https://nznaturalclothingshop.co.nz/...lothes-shrink/
here are the steps to fix it:
1. Fill your sink or basin with lukewarm water and 1/3 cup of hair conditioner
2. Pop the jumper in and let it soak for about 10 minutes
3. Drain the water out of the sink. When the sink is empty, press the jumper against the sides of the sink to rinse the jumper out, but do not wring it.
4. Put down an absorbent towel, lay the item flat on top of it and lay another towel on top. Press gently to dry the jumper.
5. Stretch the jumper back into its original shape.
6. Keep the item lying flat in a very well ventilated area until dry.