You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How can I help you?

USER: I want to change my existing reservation, can you please help me?

ASSISTANT: Sure, may I know your name please?

USER: My name is Cynthia Lopez.

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

USER: No problem, thank you for checking.

ASSISTANT: Thank you for choosing us.