To enter withholding there should be a little box - I have other boxes on my 1099B to enter.
Or Enter withholding on forms (like a 1099B) other than a W2 or 1099R under
Federal Taxes (or Personal for H&B)
Deductions and Credits
Then scroll way down to Estimates and Other Taxes Paid
Other Income Taxes - Click the Start or Update button
Next page scroll down to bottom section Other Income Taxes Paid
Click Start or Update by Withholding not already entered on a W-2 or 1099