As answered above you don't enter it. Turbo Tax automatically puts half of your self employment tax on 1040 Schedule 1 line 14.
The SE tax is already included in your tax due or reduced your refund. It is on the 1040 Schedule 2 line 4 which goes to 1040 line 15. The SE tax is in addition to your regular income tax on the net profit. You do get to take off the 50% ER portion of the SE tax as an adjustment on 1040 Schedule 1 line 14 which flows to 1040 line 8a. Turbo Tax automatically calculates the SE Tax and Adjustment.
The 50% SE tax deduction only reduces your taxable income and regular income tax. It will not reduce your schedule C Net Profit or reduce the total self employment tax.
