You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: Alexander Parker here.

ASSISTANT: How can I help you?

USER: I want to change my existing reservation which I have have reserved with your agency due to my schedule got postponed.

ASSISTANT: I am sorry no reservation found on your name.

USER: It's ok, anyway thank you for the help.

ASSISTANT: Thank you for choosing us.

USER: Most welcome.