I amended my return because i needed to add my unemployment information but never received my 1099 form. Do I need to add it when I mail it?

Hello, I amended my return and filled out the 1040x form. I just need to mail it now but It says to add changes or documents to support. The thing is that I never received my physical 1099 , I used the information on my unemployment benefits paid page. What do I need to mail it? How do I mail it?
Thank you!!!