I have to do multiple years of taxes but when I'm logged in I'm only able to work on one year.

[SweetieJean]

TT Online is only good for 2020 returns.  Prior years (2017-2019) require that you purchase and install the desktop software for each applicable year.  Prior returns must be printed and filed by mail.

TurboTax® 2019 Tax Software for Filing Past Years’ Taxes, Prior Year Tax Preparation (intuit.com)

TurboTax® 2018 Tax Software for Filing Past Years’ Taxes, Prior Year Tax Preparation (intuit.com)

TurboTax® 2017 Tax Software for Filing Past Years’ Taxes, Prior Year Tax Preparation (intuit.com)

[DoninGA]

The TurboTax online editions are Only for tax year 2020.

To complete and file a prior tax return, 2019 thru 2017, using TurboTax you would need to purchase, download and install on a personal computer one of the desktop editions for each year required from this website - https://turbotax.intuit.com/personal-taxes/past-years-products/

A prior year tax return can only be printed and mailed, it cannot be e-filed.  If mailing multiple tax years use a separate envelope for each tax year.

[VolvoGirl]

Sorry, Online for 2019 and prior is closed now so you can not start a new 2019 or prior return or finish one. Online is only for 2020. Oct 15, was the last day to efile.  2019 is now the prior year. If you entered 2019 into the 2020 online version you should clear out your online return so you can use it for 2020.
https://ttlc.intuit.com/community/using-turbotax/help/how-do-i-clear-and-start-over-in-turbotax-onli...

Did you start an Online return? How to finish a prior year online return
https://ttlc.intuit.com/community/prior-year-return/help/how-do-i-finish-a-prior-year-return-that-i-...

Or How to file a prior year
https://ttlc.intuit.com/community/using-turbotax/help/how-do-i-prepare-a-prior-year-tax-return/00/25...

You can only buy the download for prior years. You have to buy a separate program for each year. They only sell the last 3 years. You need a full Windows or Mac computer to install it on. Buy the download here
https://turbotax.intuit.com/personal-taxes/past-years-products/

You have to print and mail prior year returns. When you mail a tax return, you need to attach any documents showing tax withheld, such as your W-2’s or any 1099’s. Use a mailing service that will track it, such as UPS or certified mail so you will know the IRS received the return. Don’t forget state.

Important! Mail Federal and State in separate envelopes and mail each year in separate envelopes.

If you are getting a refund, there is not a penalty for filing past the deadline. You have 3 years to file for a refund. If you owe taxes, the interest/penalties will be calculated by the IRS based on how much you owe and when they receive your return and payment. The IRS will bill you for this; it will not be calculated by TurboTax.

If you want to file for free you can fill out the forms by hand. Here are some basic forms…..

Here is the IRS 2019 Form 1040
https://www.irs.gov/pub/irs-prior/f1040--2019.pdf

or if you want bigger type use 1040SR for Seniors,
https://www.irs.gov/pub/irs-prior/f1040s--2019.pdf

And 2019 Instructions https://www.irs.gov/pub/irs-prior/i1040gi--2019.pdf

2019 Tax and EIC Tables
https://www.irs.gov/pub/irs-prior/i1040tt--2019.pdf

Sch 1 : https://www.irs.gov/pub/irs-prior/f1040s1--2019.pdf
Sch 2 : https://www.irs.gov/pub/irs-prior/f1040s2--2019.pdf
Sch 3 : https://www.irs.gov/pub/irs-prior/f1040s3--2019.pdf

Then when you do file 2020 enter 0 for the 2019 AGI since you are filing 2019 late.

I have links for other years too.