See this TurboTax support FAQ for completing a prior year tax return originally started with the online editions - https://ttlc.intuit.com/community/prior-year-return/help/how-do-i-finish-a-prior-year-return-that-i-...
You will have to download the CD/download software to finish preparing a 2017 return you began online. It is too late to receive a refund for a 2017 return, so even if the return shows a refund--it has been forfeited unless you had an extension for that 2017 return. If you owe tax due, you still have to pay the tax---and you can also expect a bill later for the late filing penalties and interest which will be calculated by the IRS.
The return has to be printed, signed and mailed. It cannot be e-filed.
Access the return by using the exact same account and user ID that you used to start on it.
You have to access your own account and/or print it for yourself using exactly the same account and user ID that you used when you prepared the return.
Many people have multiple TT accounts and forget how to access them. Log out of the account you are in now.
If you already paid for your online software you can ask customer support for a download of the desktop software.
They are available from 5 a.m. to 5 p.m. Pacific time Monday-Friday.