If your return has been submitted, you should wait to determine if it has been rejected or accepted.
If rejected, you can go back and change or adjust your return to include the 1099-B.
If accepted by the IRS, you should wait until you receive your refund or paid your balance due to amend the return.
You will need to print and mail the amendment along with a copy of your 1099-B (it cannot be e-filed) and allow about 16 weeks for processing.
See
How Do I Amend a Return Already Filed?