Why does the 1099-B Turbo Tax Form not allow me to update to enter the correct cost basis.

[fanfare]

In prior years, TurboTax supported basis correction as instructed by IRS . It should still support it.

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For non-covered securities ( BOX B or E) showing zero (wrong) basis, enter the correct basis yourself.
Use code "B" and put -0- in col (g).
For Box A or D, leave basis as reported, use Code "B" and put an adjustment in col(g).

@bill.wagner 

[DawnC]

You can edit the form.   

In TurboTax Online - Search for 1099-B and use the Jump to link.  Select the down arrow and then click on Edit.  See image below

In TurboTax Desktop - Search for 1099-B and use the Jump to link.   Select Review, then select the pencil icon to edit your 1099-B.

Put a checkmark in the box that says The cost basis is incorrect or missing on my 1099-B if you need to adjust the cost basis.