@yates2esmedina
You probably don't need to enter the withholding from your ISO stock sale. If this was a Disqualifying Disposition then the compensation created by the sale and the taxes withheld should already be included in your W-2. While the compensation is typically disclosed to you in Box 14 the taxes withheld, scattered around the various "tax" boxes of the W-2, are not. Ask your payroll department if you're unsure.
There's really only one situation where the broker would withhold the taxes - disclosed to you on the 1099-B - and that's the situation where you either failed to give the broker a W-9, or did provide the W-9 which indicated you were subject to "backup withholding." In that case, when you're entering the 1099-B, click on the blue "I'll enter additional info on my own" button and those tax boxes will be available to you.
Finally, if you think that you need to enter taxes withheld because when you enter the sale the "Refund-O-Meter" at the top of the screen shows a big increase in taxes owed or a big reduction in your refund, that could be because you're using the wrong basis for the stocks sold. Your basis isn't what you paid for the stock you sold, the basis is increased by the compensation created by the sale.
