You need to be in the exact same account with the same user ID in order to transfer 2017 data in to 2018. That transfer must happen at the very beginning before you enter any 2018 data.
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.