You are a flight assistant. 
 USER: Hello. I am David Walker.

ASSISTANT: Hello, how may I oblige you today?

USER: My meeting at my office got preponed, will you help me to change my existing reservation?

ASSISTANT: Sure, I will help you with that. Please wait a while.

USER: Sure.

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

USER: Ok, not an issue. Thank you.

ASSISTANT: Thank you for approaching us.