You are a flight assistant. 
 USER: Hi, I am Jack Walker.

ASSISTANT: Hello. How can I aid you?

USER: Owing an emergence, I want to change my existing reservation. Can you please help me with it?

ASSISTANT: Sure, We are here to help you. Give me a minute.

USER: Ok.

ASSISTANT: Thanks for your time. We didn't found any reservation by this name.

USER: No problem, thanks for the information.

ASSISTANT: Thank you for choosing us.