I did my taxes this year 2019 but just found out I had to file for 2017 because my husbands w2s are from 2016. How do I cancel my 2019 and do it for 2017?

Yikes.  First let's get the years straight.  This year we did our 2018 return for the year ending Dec 31, 2018.  So if you have 2016 W2s you need to file a 2016 return or amend it if you filed.   Then what about 2017?  Did you file a 2017 return last year for income earned in 2017?

Now for the 2018 return you just filed with the 2016 W2s.  Did you efile?  Was it accepted?   You can check your efile status here     

https://turbotax.intuit.com/tax-tools/efile-status-lookup/   

if it was Accepted you have a problem.  Hopefully it will reject so you can fix it.

The current tax year is 2018, not 2019 (2019 tax will be filed next year in 2020).

E-file and online file for 2016 (which is the tax year for a 2016 W-2) is closed.  2016 can only be paper filed using the Windows or Mac desktop software installed on your computer if you wish to use TurboTax.

You can purchase 2016 here:

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