The only way to file them for free now is to prepare them by hand on paper and mail them in. If you want to use tax software you have to purchase it.
To file a return for a prior tax year
If you need to prepare a return for 2015, 2016, or 2017 you can purchase and download desktop software to do it, then print, sign, and mail the return(s)
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 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.
PRIOR YEAR FORMS FROM IRS
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
Form 1040EZ Instructions https://www.irs.gov/pub/irs-pdf/i1040ez.pdf