You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I help you today?

USER: I would like to change my existing reservation, can you help me in that?

ASSISTANT: Sure, Let me know your name to check your reservation?

USER: Sure, myself Margaret Hall.

ASSISTANT: Ok, please wait a moment.

USER: Sure, 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 ok, no problem. Thank you for the information.

ASSISTANT: Thank you for choosing us.