You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how can I help you today?

USER: Could you please change my existing reservation?

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

USER: I am David Baker.

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

USER: Not a problem, thank you for the information.

ASSISTANT: Thank you for choosing us.