I'd be glad to guide you through the steps in deleting the other QuickBooks Online (QBO) account associated with your client, David.
To initiate the account deletion process, you must cancel the account's subscription first since the system will remove the account from its records one year after cancellation. If the account was purchased online directly from Intuit, please refer to the steps below:
Open a web browser on your computer, not a mobile device.
Sign in to QBO as the primary company admin.
Go to Settings and select Subscriptions and billing.
Locate the account and click Cancel or Cancel subscription. If you're canceling a trial, hit Cancel your trial.