Thank you for using Turbotax.
If you have missed out your 1099 B , you need to amend your tax return . However amend option in Turbotax will be available depending on the availability of 1099 X form availability.
Please check the following for Forms availability date:
https://ttlc.intuit.com/questions/1908854-irs-forms-availability-table-for-turbotax-individual-perso...
