You are trying to add a new charge card to QuickBooks but you are receiving an error that states "already has a log in associated with American Express." The solution to this problem is to reset the bank feeds in QuickBooks when there are changes in your bank account.
- Select Banking > Bank Feeds > Bank Feeds Center.
- Click Disable bank feeds.
- Modify the account customer id to reflect the new bank login id.
Save and close.
Note: This does not work unless you have exclusive access to online banking.