You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I help you?

USER: I want to change my existing reservation, due to some work at my office. Can you please change my existing reservation?

ASSISTANT: I am here to help you, may I know your name to check your reservation?

USER: Sure, I am Joshua Lopez.

ASSISTANT: Ok, please wait.

USER: Ok.

ASSISTANT: Sorry, there is no reservation found on your name.

USER: Ok, Thank you for your help.

ASSISTANT: Welcome Joshua Lopez.