You have to know the User ID and password that was used for the 2017 TurboTax online account to access that account. If you do not have access to that information then you would have to contact TurboTax support and go through the process to prove your identity as is shown on the tax return.
You can also get free transcripts of your federal return from the IRS - http://www.irs.gov/Individuals/Get-Transcript
See this TurboTax support FAQ on how to contact Support - https://ttlc.intuit.com/questions/3401489
Use this website to contact TurboTax support during business hours - https://support.turbotax.intuit.com/contact/
Support can also be reached by messaging them on these pages https://www.facebook.com/turbotax/ and https://twitter.com/TeamTurboTax
