There are two things that I can think of for this, mad2331.
If you're trying to delete your QuickBooks Self-Employed account, we'll have to cancel it. After a year of being canceled, it will automatically be deleted. You'll still have read-only access though for a year.
Here's how to cancel:
Click the Gear icon.
Select Billing Info, then Cancel subscription.
Afterward, you'll receive an email that confirms your cancellation.
If you're trying to delete a bank account, I'll show you how:
From the Gear icon, select Bank Accounts.
Select the account you want to delete.
Select the Trash can icon.
Type Delete to confirm.
When you're ready, select Delete.
I've added these articles for more information when deleting a QBSE or bank account: