To transfer prior year 2018 tax data to the 2019 tax return you will have to clear your 2019 tax return and start over.
If you have not paid for the online edition you are using, have not filed your tax return or registered the Free edition, then you can clear your return and start over. Click on Tax Tools on the left side of the program screen while working on the 2019 online tax return. Click on Clear & Start Over.
See this TurboTax support FAQ for transferring a prior year to the 2019 online editions - https://ttlc.intuit.com/community/entering-importing/help/how-do-i-transfer-last-year-s-return-into-...