Hi there, @ovvnnes.
You can let your employee add you as an authorized user in their online banking. This will allow you to link their American Express Credit Card to QuickBooks Online (QBO). Once done, here's how to add AMEX Credit Card to the QBO Banking page.
First, let's create an account for AMEX Bank in the Chart of Accounts (COA) menu. Here's how:
- Go to Settings, select Chart of Accounts.
- Click on the New button.
- Fill in the following information:
- Account Type
- Detail Type
- Name
- Description (Optional)
- Enter Opening Balance (Optional)
4. Select Save and close.
After that, you can go to the Banking menu to link the AMEX CC. Here's how to link:
- Go to the Transactions and select the Banking menu.
- Select the + Link Account button and enter AMEX in the search field.
- Click the bank that fits the AMEX CC description and select Continue.
- There will be a pop-up window to let you log in to the AMEX account.
- Follow the on-screen instruction.
- Select which account you want to connect.
- Click on the drop-down button beside the account and select the account you've made in COA.
- Select Connect.
I've added some screenshots for additional reference.

For more information about the process of connecting your bank to QBO, you can check out this article: Connect your American Express Business account to QuickBooks Online.
I've also included this article for your future task when your ready to reconcile you're account: Reconcile an account in QuickBooks Online. This contains a lot of tips whenever you need to undo reconciling or reconcile an account connected to online banking.
Please don't hesitate to let me know in the comment section below if you need further assistance. I'd be happy to back you up. Take care and have a wonderful day.