How do I import last years return without erasing what I have already entered for 2023?

Sorry, that is not possible.  You can only transfer the 2022 tax return when you first start the 2023 tax return using the online editions.  If you used the TurboTax online editions for tax year 2022, then you should have signed  onto the 2023 online account with the same UserID you used for the 2022 account.

If you used the TurboTax desktop editions for the 2022 return then see this TurboTax support FAQ for how to transfer the 2022 return to the 2023 online editions - https://ttlc.intuit.com/turbotax-support/en-us/help-article/import-export-data-files/transfer-last-year-return-turbotax-online/L279eUvY2_US_en_US?uid=m26evc24

You will have to clear the tax return and start over to transfer the 2022 return.

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 with a lower priced edition. Click on Tax Tools on the left side of the program screen while working on the 2023 online tax return. Click on Clear & Start Over.