First, I would like to know if you meant about your Bank account connected with QuickBooks Online (QBO) or is it about the account in your Chart of Accounts. Some additional details would be very helpful.
If you meant on how to delete your Bank Account, let's make sure that the bank is not connected with our online banking feature. If so, you can disconnect it first. Here's how:
In your QBO company, go to the Hamburger icon and click on the Transactions tab.
Select Banking tab and click on the Edit icon.
Select Edit account info tab.
Tick the box for Disconnect this account on save.
Hit Save and Close.
I added a screenshot for your reference.
Now, your account is still in QuickBooks but it will not automatically upload bank transactions. To delete your account in Chart of Accounts, you may need to consult your accountant first if you need more information about the impact in your books. You can also share these steps with your accountant:
In your QBO company, click on the Gear icon and select Chart of Accounts.
Find the account that you want to delete in the list.
Click on the drop-down button along the Account name and select Delete.
You'll receive a message, "Are you sure you want to delete this?", click Yes.