I did not file in 2017 & still need to do so. Can I do that online?

No. You would have to use a TurboTax prior tax year product, which requires installation.

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

Online preparation and e-filing for 2017 is permanently closed.

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)

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.