See this TurboTax support FAQ for completing a 2018 tax return originally started using the online editions - https://ttlc.intuit.com/community/prior-year-return/help/how-do-i-finish-a-prior-year-return-that-i-...
You missed the October 15, 2019 deadline. You will not be able to use online TurboTax now. If you started in online, you now need to switch to desktop software which must be downloaded to a full PC or Mac. Your return cannot be e-filed; it will have to be printed, signed and mailed.
Online preparation and e-filing for 2018 is permanently closed. You have to download 2018 software to a full PC or Mac (not to a mobile device) and then print, sign and mail your return. If you already paid for your TurboTax software, you can contact customer support to push a download of the software to you.
To call TurboTax customer support
They are available from 5 a.m. to 5 p.m. Pacific time.
To finish a prior year return started in TT online:https://ttlc.intuit.com/questions/2559403-how-do-i-finish-a-prior-year-return-that-i-started-in-turb
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 and/or your state received the return.