You need to start with the oldest return first. TurboTax only supports their software for the current tax filing year and 3 years back. So the farthest back you can go with TurboTax right now is the 2016 tax return. For earlier years you'll need to get the blank forms from the IRS website and do them manually yourself, or seek professional help.
Even if you can get TurboTax for years prior to 2016, you can not get the *REQUIRED* corrections and updates to the program. So chances are high the return would be wrong anyway. TurboTax does not and will not honor their 100% accuracy guarantee for tax years prior to 2016 either. Additionally, if you are due a refund the IRS has a 3 year statute of limitations on that. So any refunds due for tax years 2015 and prior will not be paid.
Finally, 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.
