You'll need to cancel your subscription to delete your QuickBooks account.
Here's how:
Sign in to your account as an admin user.
Click the Gear icon and choose Account and Settings.
Go to the Billing and subscription tab.
In the QuickBooks section, click on Cancel Subscription.
Follow the steps on the screen to cancel your subscription.
Choose to Submit cancel subscription.
Hit Got it.
Once your account is canceled, you're given read-only access to your QuickBooks account for one year until it is completely deleted. For additional information, you can check this article: What happens to my QuickBooks Online data after I cancel?. This also provides details about the export policies after cancelation.