You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How may I be of your service?

USER: I need to change my existing reservation, Can you please help me with that?

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

USER: Sure.

ASSISTANT:  I need some basic information to check your ticket details, can you please tell me your full name?

USER: Kevin Lee here.

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

USER: Sure.

ASSISTANT: I am very sorry to inform you that there is no reservation found under your name in our database.

USER: Ok, no problem.

ASSISTANT: Thank you for approaching us.

USER: Thanks for your information.