Amending return

Hello, I already e-filed my taxes and got my return but a new W2 came in the mail. It’s from an employer that I did NOT work for in 2019 but did receive a severance from in the beginning of 2019. I’m assuming that’s what it’s for? How do I go about adding that to my return this year? I read that I would have to submit an amendment form. But where can I access that and how do I send it in? Also, will it effect the money I already got back? Thanks!