It's part of the bobbin winder. You don't need it to sew. If you have a metal shop in your town, it can be fixed with little cost. They will have the epoxy to bond the metal and you will hardly notice it had been broken off. Try a body shop if no metal shop is close by. I would contact the seller and send pictures. The seller did not package it carefully enough and there should have been insurance on it too. The seller should pay for repairs or refund a big part of the purchase price and she will have to deal with the shipper, not you.