After you file

If you entered 2018 W2 into the 2019 Online version You can try to clear and start over

https://ttlc.intuit.com/community/using-turbotax/help/how-do-i-clear-and-start-over-in-turbotax-onli...

 

Or you can leave this account and set up a new account to do 2019.   How to start another return in the Online version

https://ttlc.intuit.com/community/using-turbotax/help/how-do-i-start-another-return-in-turbotax-onli...