You can try to clear you return but you can not delete your account. How to delete/clear your Online return
https://ttlc.intuit.com/community/using-turbotax/help/how-do-i-clear-and-start-over-in-turbotax-online/00/26444
If you want to completely deactive your account you need to call in and get a case number.
Contact Customer Service
5am-5pm Pacific Time Monday -Friday
https://support.turbotax.intuit.com/contact/
What is the Turbo Tax phone number
https://ttlc.intuit.com/community/using-turbotax/help/what-is-the-turbotax-phone-number/00/25632
You cannot delete or disable your account. Customer service will not give you a case number. They called the information in this answer "completely incorrect" and said removing an account was a "physical impossibility".
Their advice was to delete files, one by one, if you can get past the 'internet connection bug' which is not a technical problem or faulty connection and has been a problem for a year.
I was left on hold for 36 minutes, by "management, well, kind of a senior person" who I could hear on a personal call in the background "What are you eating?, Is it good?" They she hung up on me.
The online ratings for TurboTax tell the full story. 1.3 out of 5 stars on sitejabber and 1.4 out of 5 on trustpilot, with less than 3% of reviews being positive. 132 negative or strongly negative to 12 positive or neutral.