You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I help you?

USER: David Hill here. Due to inconvenience of my work, I want to change my reservation. Can you please help me for that?

ASSISTANT: Sure, I will help you out. Please wait for a while.

USER: Ok, I will wait.

ASSISTANT: Sorry, there are no reservations found.

USER: Anyway, thanks for the information.

ASSISTANT: Thank you for choosing us.