I use this wash on my hand knits: https://www.amazon.com/gp/product/B001W93UWS/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

It should help soften the sweater. It will also stop shedding over time. Another thing you can try is freezing the sweater, place it in a plastic bag and put it in the freezer for a few days. This can also help from what I've heard.