Yes, you can use TurboTax to prepare an amended return, even if you didn't file the original return using TurboTax. Please follow the instructions in this TurboTax FAQ to prepare the amended return. Once you've selected the year you want to amend, please select the option to amend using CD/downloaded software.
These instructions assume that you prepared your return using TurboTax. Since that's not the case, you'll need to enter the information from your return as originally filed, then proceed to start in Step 3.
