https://proconnect.intuit.com/community/accounting/help/1099-b-proceeds-from-broker-and-barter-excha...

1. Go to the Schedule D/4797/etc screen where you entered the box 1 amounts for this transaction.
2. Click the Details button.
3. From the top of the screen, select the Schedule D section.
4. Enter the box 4 amount in Federal income tax withheld.