If the shares were sold, you do need to report them and there should be a 1099-B. Form 3921 is given when you exercise your ISO and you hold on to it until you sell the stock. When sold, you get a 1099-B. If the new company exercised your old stock to trade for the new company stock, that would make sense. It would not be a sale, just an exchange/ takeover/merge to make your stock part of theirs.
You should verify that your stock was not converted into the new company stock rather than sold. There are so many variations on how a deal can be structured with the acquisition. You should ask the new company what was done and how to handle it.
If sold, you have the sales price and basis, acquisition date and sale date. That should be everything you need to report the sale. If the program is determined the income is in your w2, you have to switch to reporting it under other income. I believe the program allows you to mark not in the w2 now. The program gets updates each week all season so things can vary.
**Say "Thanks" by clicking the thumb icon in a post
**Mark the post that answers your question by clicking on "Mark as Best Answer"
