You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I help you?

USER: My name is Christopher Hernandez here. I would like to change an existing reservation.

ASSISTANT: Please give me a moment to check your ticket status.

USER: Sure, take your time.

ASSISTANT: Sorry, no reservation is available by your name.

USER: No problem. Thank you for the information.

ASSISTANT: Thank you for choosing us.