You can stop QuickBooks to download your bank transactions automatically by disconnecting your online banking connection. Before doing so, you'll first need to make sure to add transactions from the For Review tab.
Once done adding, you can proceed to disconnect your bank account. Here's how:
In the left menu, click Banking and go to the Banking tab.
Select the blue tile for the AMEX bank account.
Hit the Edit pencil icon.
Choose Edit account info.
Remove the checkmark beside Disconnect this account on save.