How can I gain access to my 2015 unfinished return so I can complete it? I do not have the exact check-in information so I can't do what the prompt suggests?

I don't have the check- in information from last year and need access to my unfinished tax return for 2015. Can you please assist me?

After you file

Use this TurboTax account recovery website to get a list of user ID's for an email address.  Run the tool against any email addresses you may have used https://myturbotax.intuit.com/account-recovery/

To finish 2015, you have to download the .tax2015 file and open it in the 2015 Desktop program installed on your computer.  If you paid for the Online version you can call in and ask for the Desktop program to finish.  You have to print and mail prior year returns.  

Here's how to finish
https://ttlc.intuit.com/replies/4186197