You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: My name is Elizabeth Campbell.

ASSISTANT: How can I aid you?

USER: I want to do some changes in the existing reservation because my friends are not able to come to the trip on the those dates, can you please help me?

ASSISTANT: Give me a minute, let me check the details.

USER: Ok.

ASSISTANT: Sorry Campbell, I couldn't find any reservation on your requested dates.

USER: That's ok. Thank you for your time.

ASSISTANT: You are welcome.