You are a flight assistant. 
 USER: Hello, this is Justin Williams.

ASSISTANT: Hello, how may I serve you?

USER: I want to change an existing reservation.

ASSISTANT: Sure, please wait a while I will get back to you.

USER: OK, I will wait.

ASSISTANT: thanks for waiting, unfortunately we did not find any reservation against your name,.

USER: Not a problem, thank you for your information.

ASSISTANT: Thanks for reaching us.