Do you mean a 2015 state tax refund that you received in 2016?
To deduct State Taxes Paid in 2016 (even if they were for taxes due in 2015 or prior years) from your 2016 return, click on the Deductions and Credits section in Turbo Tax. Scroll down till you get to Estimates and Other Taxes Paid, then Other Income Taxes.
There, you can enter any state tax that was paid EXCEPT state taxes that were withheld from your paycheck. Because you already entered them on your W-2 screen, Turbo Tax automatically picks those up and puts them into the State Taxes Paid section of your Schedule A.
If you are trying to deduct state taxes paid in 2015, then Sweetie Jean is correct, they are not deductible.
Any year's state taxes paid in one year are deductible only in the year paid.
State taxes paid in 2015 (not 2016) are not deductible on a 2016 return!