Hi there, @MelissaLM. I'll guide you how to remove the customer's bank information in QuickBooks Online.

An option to hide a customer's bank details is to replace them with a dummy account or non-transacting card number since deleting them is not yet available in QuickBooks.

consider these steps below:

1. Sign in to your QuickBooks.
2. Select Sales, then Customers from the left navigation bar.
3. Choose the customer name, then click Edit.
4. Go to the Payment and billing tab.
5. Choose the credit card number or bank under the Preferred payment method field.
6. Click Add on the Credit Card Information window.
7. Change the following:

• Credit card number: 4111-0001-0001-0001. This is a non-transacting test card number.
• Expiration date: Any future date.

Your customer's saved bank details will be deleted by the updates. 

Alternatively, I added this article for your future reference:

• Add and manage customers in QuickBooks Online.
• Edit customer information.
• Create invoices in QuickBooks Online.

Hit reply if you need additional help. Have a great day!