My1099-B form has a column called "Applicable check box on Form 8949" with an X in it. How can I enter it into Turbotax?

[JohnW152]

You don't actually enter this X anywhere. 

It indicates that your broker doesn't know whether the gain or loss reported on your Form 1099-B is a short-term or long-term gain or loss. You'll need to use your personal records to determine whether your gain or loss on this transaction is short-term or long-term.

According to Form 1099-B in the Instructions for Form 8949:

If you received a Form 1099-B (or substitute statement) for a transaction, box 2 may help you determine whether your gain (or loss) is short term, long term, or subject to special rules. If box 2 is blank and code X is in the "Applicable checkbox on Form 8949" box near the top of Form 1099-B, your broker doesn't know whether your gain (or loss) is short term or long term. Use your own records to determine whether your gain (or loss) is short term or long term.