From that screen, clicking “Add existing user” should yield a screen with BLANK fields. If not, either your system is auto-populating fields (no good) or your user profile is still saved on your system. You need to delete that from the system entirely. (not sure how do on Windows/Mac - I’m using a tablet that nukes all user data if uninstalling the app)
Glad you resolved it! You typed that just as I was typing a follow-up: indeed, the folder where Zwift was storing your user data needs to be removed or the newly reinstalled app will just keep trying to pull old profile data.
Great news that this worked for you, Ratna.
To help others find what worked thanks to @Otto_Destruct, you can select the most useful of his responses and tag it as ‘Solution’. That will add the relevant info just below your opening post.
It’s hard to say if the issue you encountered is a true Zwift bug or if it’s more an issue with macOS.
My first thought is that you’ve got the email and password stored in your keychain, which is an encrypted container that securely stores your account names and passwords on a Mac. I’m guessing you’ll need to clear Zwift data out of that, which generally takes more than deleting folders and re-installing Zwift.
For more information on managing your passwords using keychains on a Mac, please see this related Apple support article.