how to download last year tax I just prepared ?

What tax year?  If you are referring to tax year 2023 that tax return can only be completed using the TurboTax desktop editions installed on a personal computer.

The TurboTax online editions are only for tax year 2024 and cannot be changed.

To access your prior year online tax returns sign onto the TurboTax website with the User ID you used to create the account - https://myturbotax.intuit.com/

Start the 2024 online tax return by entering some personal information then click on Tax Home on the left side of the screen.

On the Tax Home webpage -

Scroll down to the section Your tax returns & documents.  Click on the Year and Click on Download/print return (PDF)