The ISO adjustment would be the amount of discount you received on the acquisition of the stock. In other words, the difference between what you paid for the stock and what the fair market value of it was when you acquired it. That would be reflected on the Form 3921. It would be box 4 on your Form 3921 less box 3 times the number of shares sold. If you held the stock more than one year, you would enter it in the long-term gain box, otherwise enter it in the short-term gain box. Enter it as a negative number.
It probably won't affect your taxes, as it pertains to alternative minimum tax, that most tax filers aren't subject to.
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