You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how may I help you today?

USER: Can you please change my existing reservation?

ASSISTANT: Sure, may I know your name please?

USER: I am Charles Davis.

ASSISTANT: Please wait for a minute, I will check the reservation list and get back to you.

USER: Sure.

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

USER: Ok, Thanks for the information.

ASSISTANT: Thank you for choosing us.