Login to the account that you used to purchase TurboTax

1. Click Intuit Account at lower left of screen
2. Click Products and Billing
3. Find your TurboTax version and download it.

Do I need to pay a second time for the download to the new PC? I have already filed 2020 return using my old PC but I want to continue to use the "Planner" feature on my new PC, with data from my 2021 Investment statements, to estimate taxes for 2021.

No, you do not have to pay again.