ERROR MESSAGE an existing quickbooks account is already linked to a bank account

Let me help you get past the error message, Warrenlogistics-.
 

You get this message when you connect both parent and sub-accounts. You're unable to connect both at the same time. You'll only have to link the account where the transactions are downloaded. If they will be downloaded to the parent account, then you'll have to connect it. If they'll be added to the sub-accounts, then you'll have to connect them instead. 

Feel free to check this article for more information: About bank or credit card subaccount setup.

If there's anything else that you need, don't hesitate to let us know. Keep safe!