If you had more than $5000 in start-up costs, the remainder is entered under Assets/Depreciation as a capital asset for amortization (TurboTax provides this category for you) over 15 years. TurboTax would have done this for you with proper entry last year. Check that you don't already have an asset listed that's presently being amortized in your 2017 return.
Otherwise, enter it on your return under the Asset category, amortized over 15 years.
If you have additional questions or details regarding this, please feel free to post in the comments for further clarification.
