After you file

In order to file returns for those years you must have your income information.  You cannot file without it.

Here are some ways to get your income information:

W-2's come from your employer,

You might need to phone, email and/or snail mail an old employer to make sure they know where to send your W-2.

https://ttlc.intuit.com/questions/2561916-how-can-i-get-a-copy-of-my-w-2

Other ways to get W-2’s:

Pay Social Security $86 per W-2:

https://www.irs.gov/help-resources/tools-faqs/faqs-for-individuals/frequently-asked-tax-questions-an...

You can get a wage and income transcript from the IRS:  It will not show the actual W-2, 1099’s, etc, but will show the income information the IRS received.  It will not, however, show your state information. It will only show the federal information.

https://www.irs.gov/individuals/get-transcript

As for filing the returns:

Each tax year has to be filed separately using the forms for the specific tax year.  They cannot be combined in any way--do not even put them in the same envelope when you mail them.  Software for past years is available back to 2016.  Any earlier years can only be prepared on paper forms by hand--and those refunds have been forfeited now.

The current online program can only be used for a 2019 return--no other year.  And if you did not file a 2018 return you will have trouble e-filing 2019.  When it asks for your 2018 AGI try using zero.  If zero does not work then you have to print, sign and mail 2019.

Online preparation and e-filing for 2018 is permanently closed.

To file a return for a prior tax year

If you need to prepare a return for 2016, 2017, or 2018 you can purchase and download desktop software to do it, then print, sign,  and mail the return(s)

https://turbotax.intuit.com/personal-taxes/past-years-products/

Remember to prepare your state return as well—if you live in a state that has a state income tax.

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/state received the return.

Note:  The desktop software you need to prepare the prior year return must be installed/downloaded to a full PC or Mac.  It cannot be used on a mobile device.

If you are getting a refund, there is not a penalty for filing past the deadline.  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.

https://ttlc.intuit.com/questions/1900990-how-do-i-file-a-prior-year-tax-return

Or you can use the paper forms and prepare them by hand to mail in:

2016

Form 1040  https://www.irs.gov/pub/irs-prior/f1040--2016.pdf

Form 1040 Instructions https://www.irs.gov/pub/irs-prior/i1040gi--2016.pdf

Form 1040A https://www.irs.gov/pub/irs-pdf/f1040a.pdf

Form 1040AInstructions https://www.irs.gov/pub/irs-prior/i1040a--2016.pdf

Form1040EZ https://www.irs.gov/pub/irs-prior/i1040gi--2016.pdf

Form 1040EZ Instructions  https://www.irs.gov/pub/irs-pdf/i1040ez.pdf

2017

https://www.irs.gov/pub/irs-pdf/f1040.pdf

https://www.irs.gov/pub/irs-pdf/i1040gi.pdf

https://www.irs.gov/pub/irs-prior/f1040a--2017.pdf

https://www.irs.gov/pub/irs-prior/i1040a--2017.pdf

https://www.irs.gov/pub/irs-prior/f1040ez--2017.pdf

https://www.irs.gov/pub/irs-prior/i1040ez--2017.pdf

2018 Form 1040, Schedules and Instructions

https://www.irs.gov/pub/irs-prior/f1040--2018.pdf
 https://www.irs.gov/pub/irs-prior/i1040gi--2018.pdf
2018 Tax and EIC Tables https://www.irs.gov/pub/irs-prior/i1040tt--2018.pdf

IRS 2018 Schedules 1 thru 6 (only if needed)
Sch 1 : https://www.irs.gov/pub/irs-prior/f1040s1--2018.pdf
Sch 2 : https://www.irs.gov/pub/irs-prior/f1040s2--2018.pdf
Sch 3 : https://www.irs.gov/pub/irs-prior/f1040s3--2018.pdf
Sch 4 : https://www.irs.gov/pub/irs-prior/f1040s4--2018.pdf
Sch 5 : https://www.irs.gov/pub/irs-prior/f1040s5--2018.pdf
Sch 6 : https://www.irs.gov/pub/irs-prior/f1040s6--2018.pdf

https://www.irs.gov/filing/where-to-file-paper-tax-returns-with-or-without-a-payment