American Express multiple connections issue

You don't have to disconnect the other account, landerson00.

Let's add the third bank account by following these steps:

1. Click Banking located at the top, and go to Bank Feeds.
2. Select Set Up Bank Feeds for an Account.
3. If there are open windows, you'll get a prompt to close them temporarily. Click Yes to confirm.
4. In the Bank Feed Setup window, enter your bank’s name on the search field, or click the American Express link under Or choose from these popular banks section.
5. Enter the User ID and Password, and click the Connect button. 
6. Follow the on-screen instructions until finished.

I've got some sample screenshot for reference here:

I'm also adding this article for more details: Set up account for Bank Feeds.

After the account is connected and the transactions are downloaded, you can now add or match them.

I'll be around if you need more help with banking in QuickBooks Desktop. Thanks.