You can no longer use TurboTax Online to file for 2017. TurboTax Online is only for the current tax year, which is now 2018. To file for 2017 you have to use the CD or download TurboTax software for 2017. Did you start your 2017 tax return in TurboTax Online, and now need to complete it, or did you never start it?
If you started your 2017 tax return in TurboTax Online, go to the following link for instructions.
https://ttlc.intuit.com/questions/2559403-how-do-i-finish-a-prior-year-return-that-i-started-in-turb...
If you did not yet start your 2017 tax return, go to the following link for instructions.
https://ttlc.intuit.com/questions/1900990-how-do-i-file-a-prior-year-tax-return
In either case, tax returns for past years cannot be e-filed. You will have to print your 2017 tax return, sign it, and file it by mail.