Are you using the Online version? You can only transfer from 2018 at the very beginning before you start so you would have to clear your whole 2019 return and start over. Are you in the same account as 2018? It's common to end up with multiple online accounts. You might have marked schedule C as FINAL in 2018 so it didn't transfer.
For the Desktop program....
If you used the Desktop program last year, see if you have another .tax2018 file on your computer.
Here's an idea. Do you still have 2018 installed? Try opening the 2018 program and see if you can get your 2018 return to show up in it and if it is the right return. Go to FILE - OPEN. And see if your schedule C is in it and if it's marked as finally disposed. Or any Assets were disposed or sold.
Then save it again with a name and place you can find. Go to File - Save As. Then start a new 2019 return FILE-NEW and transfer from the saved 2018 file.