Online Banking helps us manage our businesses, LongChurn.

Before disconnecting your bank account from QuickBooks Online, we'll need to make sure that duplicate entries  are taken care of.

We'll need to undo the banking transactions that were added or matched and caused the duplicate issue.

1. In the Banking page, go to the Reviewed section.
2. Mark the added or matched transactions and click the Undo button.

After that, we can already disconnect your bank account:

1. In the Banking page, highlight the bank account you want to disconnect.
2. Click the pencil icon and select Edit account info.
3. In the Account window, mark the Disconnect this account on save box.
4. Click Save and Close.

Now, you'll need to use a valid WebConnect file when manually uploading your banking transactions. You can download it from your bank's website.

Then, you can follow the steps in this article to upload it: Manually Upload Transactions into QuickBooks Online.

If you decided to reconnect your bank account, then you can use this article for reference: Connect Bank and Card Accounts to QuickBooks Online.

I'll be right here if you have other concerns. Have a great day!