You'll enter the sale of the stock using the "Stocks, Mutual Funds, Bonds, Other" interview. If you use the ISO step by step process you'll be asked to enter the Form 3921 in that interview.
You'll tell TurboTax about the shares that you exercised and did no sell using the "ISO Exercise and Hold" interview. That interview, too, will ask for Form 3921 information.
Tom Young
