You can only transfer 2018 info into a new blank 2019 return. How was the 2018 return prepared (Online TurboTax versus desktop software), and what are you using for 2019? Once we know that, we can tell you some options.
If you used Online TurboTax both years, the 2018 info should have transferred in automatically if you are in the same account.
Sorry if you want to transfer from 2018 you need to start a new blank 2019 return. Go up to File-New and if it doesn't find your .tax2018 file you can browse to where it is. It should be on your hard drive not on a flash drive or external.