When you posted your question you indicated that you are using TurboTax Live Self Employed. See the tag below your question. But if that's true you cannot access the What-If Worksheet at all. Are you actually using the CD/Download TurboTax software?
You cannot modify column 1 of the What-If Worksheet. Column 1 is the figures from your actual tax return. You have to check one of the boxes at the top left to copy column 1 to one of the other columns to create a what-if scenario. You will then be able to change line 40 in column 2, 3, or 4.
