Should customer choose to apply the existing credit to an order they are placing via Desktop, the credit would automatically apply to the order.
The customer can choose if they want to use their available credit or not. They would need to untick the box next to the “Use My Credit” option to not have the credit applied.
Where can I find how much credit I have available?
Go to “My Account Dashboard” under the My Account option and your credit will be displayed under “Payment and Credits”