First of all, I'd like to thank you for allowing QuickBooks to help you with your accounting needs. I can walk you through how to delete your QBO account.
You have the option to purge your data if you want to start from scratch. This can be done if you are using the QuickBooks Essentials or Plus version, and your company file is less than 90 days old. The system deletes all data entered into the company, and you're unable to restore or reverse them.
To do that, you'll just have to edit the URL in your browser's address bar. Delete all the text after the last / and enter purgecompany.