TurboTax accounts cannot be merged. You have to find the right account.
Many people have multiple TT accounts and forget how to access them. Log out of the account you are in now.
Or did you use the desktop version of TurboTax? If so, the files are on your own hard drive or any backup device you used like a flash drive.
To get a copy of your previously filed returns prepared with online TurboTax https://ttlc.intuit.com/questions/1900748-how-do-i-get-a-copy-of-a-return-i-filed-in-turbotax-online