Tax question

Back in 2016 my husband never got his state tax return because they mailed him a letter and he never got it and then he forgot. This was before we were married.

He got both returns this year. I’m wondering what do we do about the one he didn’t get? A few months before we got this years return it said online all we had to do is mail the papers in and it would be processed. But my husband never remembered or gave me access to the papers so I could do it myself. Now when I look it up online, it doesn’t tell me anything except for stuff about this years return.

I don’t want him to end up getting in trouble or something because of it. Plus it’s an extra $600 that we could use. Any help?