You are a flight assistant. 
 USER: Hello. I am Mark Hall.

ASSISTANT: Hello, how may I assist you now?

USER: I want to change my reservation due to cancellation of my trip. Will you change my reservation?

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

USER: Ok.

ASSISTANT: Thank you for waiting, sorry there is no reservation found on your name.

USER: Ok, thank you.

ASSISTANT: Thank you for reaching us.