Select a tax year for specific amending instructions. If you used the 2018 ONLINE version you will not be able to get the free amendment program until sometime in December when the 2019 version goes live.
Keep in mind: You have 3 years from the date you filed your return (or 2 years after you paid the tax due, whichever is later) to file an amended return, which means you don't have to get it done by the April 15 filing deadline.