You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I help you today?

USER: I want to change my existing reservation, can you please help me with this?

ASSISTANT: Sure, I'll try to help you in changing an existing reservation.

USER: Thank you.

ASSISTANT: Can I have your name to check the reservation list?

USER: Christopher Moore.

ASSISTANT: Ok, please wait a minute I will get back to you with the present status.

USER: Sure.

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

USER: No problem, thank you.

ASSISTANT: Thank you for approaching us.