You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: My name is Helen Campbell.

ASSISTANT: How may I help you Campbell?

USER: I want to change an existing reservation.

ASSISTANT: Wait a moment.

USER: Ok.

ASSISTANT: Sorry, there is no reservation found with this name.

USER: That's fine, thank you for your help.

ASSISTANT: Thank you for reaching us.