If you can't find it on your depreciation worksheet, you would have to look back at the first year you placed it in service.
Given that you did this in 2015, you might not be able to. Any type of adjustment like this would either require an amended return or filing Form 3115 (change in accounting method). The new method would have to be accepted by the IRS, and then transferred to the North Carolina return.
Having said this, North Carolina does not follow the Bonus Depreciation provision allowed on the Federal return. If you used Bonus Depreciation in 2015, for example (when the amount was 50%), North Carolina would have used your original complete basis in 2015 and calculated out "normal" depreciation from that point. This creates parallel amounts of deductions, etc. between the Federal and North Carolina returns. This website provides more information: Adjustment for Bonus Depreciation - NCDOR
If you are being audited or need this information for some other reason, and the return implied was prepared by TurboTax, you may try to contact Audit Support Services for assistance.