It's just as the article quoted by George explains.

If you're preparing a F.1040 and need to disallow part of the loss for wash sale, you'd go to that transaction that need to be disallowed (partially in your case) on Screen 17.1, scroll to the line "Wash sale amount disallowed (-1 to disallow all)" and enter the amount that should be disallowed (or -1 if the entire loss should be disallowed).  This will create an adjustment for columns (f) and (g) on F.8949 for the amount of loss to be disallowed for wash sale.