Each year has to be filed separately. You can use TurboTax Online for 2019, as long as you finish by October 15, but you cannot use TurboTax Online to file for past years. TurboTax Online is only for the current tax year. To file for earlier years you have to use the CD or download TurboTax software for each year that you need. You can purchase downloads at the following link.
Past Years' Products
You might get a better price from a reputable online seller that still has TurboTax in stock for the years that you need.
Tax returns for past years cannot be e-filed. You will have to print your past-year tax returns, sign them, and file them by mail. Mail each year in a separate envelope.
