How do I enter worthless shares in a company that declared bankruptcy if I did not receive a 1099-B?

You should not indicate that you did the "The cost basis is incorrect..." because you did not receive a Form 1099-B.  You need to determine what the correct cost basis is and enter that.  Assuming you had held all the shares more than a year at the time the company filed for bankruptcy, you will have a long-term capital on all shares.  If you held any of the shares exactly one year or less, then you will have ordinary income  equal to the amount of the discount you received and short-term capital loss.  

@DavidD66 thank you for your response! I also ran into the same issue when I did not select "The cost basis is incorrect...", I tried it both ways (box checked and unchecked - same issue).

The gains and losses spreadsheet has several columns, including Acquisition Cost, Ordinary Income Recognized, and Adjusted Cost Basis. When entering the information into turbotax, I'm first prompted with field "Box 1e - Cost or other basis". I had been entering the "Acquisition Cost" from the gains and losses spreadsheet into that field. On the next page in turbotax, I am prompted to enter my "Adjusted cost basis", so I'd been entering that information from the spreadsheet into that field.

Is your suggestion to just enter "Adjusted Cost Basis" (from the spreadsheet) into the turbotax "Box 1e - Cost or other basis" field? And then not bother with the "Acquisition Cost" column from the spreadsheet, or the turbotax "Adjusted cost basis" field?

Thanks again for your help and expertise! 

Yes.  There is no need to enter a cost basis and then adjust it if you are not entering from a Form 1099-B.  Just enter the correct basis the first time.