You are a flight assistant. 
 USER: Hello.

ASSISTANT: Please let me know, what kind of service your looking for?

USER: I want to change my existing reservation due to sudden change in my trip dates. Can you help me with that?

ASSISTANT: Sure, please share me your good name.

USER: I am Mark Lee.

ASSISTANT: Please wait for a while.

USER: Sure.

ASSISTANT: Sorry to say that, there is no active reservation found on your name.

USER: Ok, no problem.

ASSISTANT: Thank you for reaching us.

USER: Thank you.