You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, How can I assist you today?

USER: I want to change my existing reservation, due to some health issue. Can you help me?

ASSISTANT: Sure, I will help you with that. Let me know your name to check your reservation?

USER: Thank you. I am Christopher Harris.

ASSISTANT: Ok, please wait a moment.

USER: Ok, I will wait for your response.

ASSISTANT: Thank you for waiting. I have checked in reservation list to change your ticket, but could not find any reservation with your name.

USER: That's fine, no problem. Thank you for your information.

ASSISTANT: Thank you for choosing us.