bank has been doubled in system

The bank may appear twice in the system due to joint account ownership, automatic linking, a technical error, previous account associations, or unauthorized access, don. However, if you want to delete the duplicate bank in QuickBooks Online, here's how to do it:

1. Go to Transactions, then Bank Transactions.
2. Select the tile for the bank account.
3. Click the pencil icon, then select Edit account info.
4. Select the Disconnect this account on the save checkbox.
5. Hit Save and Close.

Just a heads up, if QuickBooks is downloading new transactions, you won't see this option. Wait a few minutes for the update to finish and try again.
 

For your reference about the process, please see this article: Disconnect accounts connected to online banking in QuickBooks Online. 
 
Additionally, if you wish to link another bank account, follow this article: Connect bank and credit card accounts to QuickBooks Online.
 

Moreover, once you've linked your bank to QuickBooks Online, make sure to categorise and routinely reconcile the accounts to confirm they correspond with your bank statements.
 

Please return to the Community if you have further questions about bank transactions or other related concern. Keep in mind that we are always here to help. Stay safe always.