I have an account with Turbo Tax under personal/self-employed business but in 2020 I elected to change my business to an S corp. Do I open a new Turbo Tax account?

[Critter-3]

No ... you can still use the personal account for the personal return although you can downgrade to Premier by choosing Premier before you log in here :  https://turbotax.intuit.com/personal-taxes/online/   OR  switch to a downloaded version ... you will only need Deluxe (basic if you don't need a state return) https://turbotax.intuit.com/personal-taxes/cd-download/

For the corporation you need a separate program which is ONLY for windows :   https://turbotax.intuit.com/small-business-taxes/

FYI ... the business return MUST be competed first  AND the due date for the 1120S was 3/15 so unless you put the return on extension the penalties are piling up quickly ... seek local professional assistance if you don't know what you are doing to be educated and they can help with the late filing fees as well.