How do I apply NC state refund for 2018? Thanks

To apply your North Carolina refund to your next year's taxes in TurboTax, go to the screen that states, "A few things before we wrap up your state taxes".in the NC interview. Choose the option to Make Estimate Payments for next year.  You can follow the interview questions and you will have the option to apply all or part of your refund to your estimated taxes for next year. 

Could not get back to or find “A few things before----------

it does not come up automatically you have to search thru prepaying taxes.