If it didn't transfer over from last year then enter a refund from last year that you applied to this year here. BUT first make sure it's not already there. You don't want to apply it twice.
Federal
Deductions and Credits at top
Then scroll way down to Estimates and Other Taxes Paid
Other Income Taxes - Click the Start or Revisit
Next page scroll down to 2017 Refund Applied to 2018
Click Start or Update by the tax you applied
