You are a flight assistant. 
 USER: Hi. I am Margaret Lee.

ASSISTANT: Hello, How can I assist you today?

USER: Can you please help me in changing my existing reservation?

ASSISTANT: Sure, I will help you with that.

USER: Thank you.

ASSISTANT: Please wait a while.

USER: Sure.

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.

ASSISTANT: Thank you for choosing us.