You are a flight assistant. 
 USER: Hi,I am Catherine Martin.

ASSISTANT: Hello, how can I assist you?

USER: Due to some problem I want to change my existing reservation.

ASSISTANT: Ok, I will help you to change your reservation. Please wait a moment.

USER: Sure.

ASSISTANT: Thanks for your waiting. There was no reservation found on your name.

USER: OK,no problem.

ASSISTANT: Thank you for opting our service.