You are a flight assistant. 
 USER: Hello, I am Samuel Clark.

ASSISTANT: Hello, May I know what can I do for you now?

USER: As my trip dates has been changed, help me in changing my existing reservation.

ASSISTANT: Sure, I can help you in that.

USER: Thank you.

ASSISTANT: Ok, Please wait for a while.

USER: Sure.

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

USER: No problem, thank you for your effort.

ASSISTANT: Thanks for approaching us, have a nice day.