You mean you paid 2017 SC tax due when you filed your 2017 tax return in 2018? You do not amend your 2017 federal return for that. You enter it on your 2018 tax return.
The money you paid to the IRS for a previous year’s federal tax return is not deductible, so you do not enter it anywhere on your 2018 return. If you paid taxes due in 2018 to your state or local government, you can enter that by going to Federal> Deductions and Credits> Estimates and Other Taxes Paid> Other Income Taxes. You can enter the taxes you paid, but do not include any penalties or interest.