You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I help you today?

USER: I am David Taylor here. I want to visit Oakland but due to some personal issue I want to change my existing reservation can you please help me in that?

ASSISTANT: Sure, I am here to help you with that. Please wait for a moment.

USER: Ok, I will wait for your response.

ASSISTANT: Sorry to say that there is no reservation found on your name.

USER: Ok, no problem.

ASSISTANT: Thank you for consulting us.

USER: Thank you for helping me.