You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: I am David Hernandez.

ASSISTANT: How may I guidance to you at this time?

USER: I am planning to change my reservation.

ASSISTANT: Sure, I am gleeful to help you, please give me some time to check your previous booking. When I have to search your ticket booking name in our previous list there is no ticket found for the name.

USER: That's ok. Thank you.

ASSISTANT: Thank you for reaching us, have a great day.