You can change API easily by visiting http://www.eurotunnel.com/apis. Simply log in with the booking reference and password detailed in your booking confirmation.
See our how-to guides for more information
Please note we only require your API information for the Folkestone to Calais part of your journey. We do not require API information for the Calais to Folkestone part of a return trip, or trips that are Calais to Folkestone only.