How do i change the bank account details as i have switched banks?

Hello there, @Andy11.

Let's add your new bank account to your chart of accounts, connect it to online banking, and manage the old one in QuickBooks Online (QBO).

The chart of accounts is a list of all of your accounts in QBO. To keep it organised, you'll need to create a new account for the current bank before managing the old one. To do this, here's how:

1. Go to Settings ⚙ and select Chart of Accounts.
2. Select New to create a new account.
3. In the Account Type dropdown, choose an account type.
4. In the Detail Type dropdown, select the detail type that best fits the transactions you want to track. 
5. Give your new account a name.
6. Add a description.
7. If this is a sub-account of an existing account, select Is sub-account and enter the parent account. 
8. Now let's make sure the account in QuickBooks matches your real-life bank or credit card account. Choose when you want to start tracking your finances. In the Balance field, enter the amount in the account, and determine the as of date. Enter today's date if you want to start tracking immediately.
9. When you're done, select Save and Close.

When you're done, connect your new bank account to online banking, so QuickBooks automatically downloads your most recent transactions. All you to do is review and categorise them to keep your financial data accurate.

Once everything is all set, you can make the old bank account inactive after your next reconciliation. Feel free to refer to this article for the complete guide: Make an account inactive on your chart of accounts in QuickBooks Online.

Also, I encourage you to reconcile your accounts regularly (every month). This helps you monitor your income and expense transactions and detect any possible errors accordingly. You may want to check out this article as your reference to guide you in doing and fixing a reconciliation in QBO: Learn the reconcile workflow in QuickBooks.

Let me know if you have other banking concerns or questions about managing transactions in QBO. I'll gladly help. Take care, and have a great day, @Andy11.