If by "last year's taxes" you are referring to a 2018 tax return. You can not use the online version of TurboTax to file a prior year tax return. You have to purchase the CD/Desktop version and physically install it on your MAC or Windows computer. Then use the program you installed to complete your 2018 tax return. Additionally, a prior year tax return can not be e-filed. The IRS says so. You have to print, sign and mail it to the IRS. You should also complete and mail your 2018 tax return before you even start your 2019 tax return.
You can purchase the CD/Download version of TurboTax 2018 at https://turbotax.intuit.com/personal-taxes/past-years-products/
