I want to delete one of bank account details

Welcome to the Community, emliefting-gmail.

Let me guide you in removing a bank account in QuickBooks Online.

To delete a bank account: 

1. Go to Transactions and select Banking.
2. Once on the Transactions tab, select the Bank Account you want to delete.
3. Click the Pencil on the top right of the Account.
4. Select Edit Account Info.
5. Scroll to the bottom and tick the Disconnect this Account on Save box.
6. Select Save and Close.

Once done, the account will no longer appear in the transaction screen. However, the chart of account will still be active in the Accounting tab.

Feel free to leave a comment if you still need help. I'll be here to assist. Have a good day!