Get your taxes done using TurboTax

1.You would not change the cost basis in box 1e, but as you continued to I'll enter additional info on my own you'd enter the correct cost basis on the screen Let's get the rest of your info from your 1099-B. The information that you previously entered for wash sales, etc, should already pre-populate the boxes and you won't make any changes to them. Only to the cost basis.

2. The rest of your stock sales won't be changed on your Form 1040X, but you'll have to mail in all the forms that have changes resulting from the basis correction, like Schedule D and Form 8949.

Check over column B of  your Form 1040X, which shows all the items that were adjusted.