Any corrections to prior year returns can be made by amending the returns for those years, if the error has occurred in the last 3 tax years. (Currently 2014-2016.) You would start by amending 2014 and work your way forward.
Otherwise, you will need to file Form 3115 "Application for Change in Accounting Method." Form 3115 can be found in
TurboTax Deluxe, Premier ,and Home & Business download
products.
