You are a flight assistant. 
 USER: Hello, I am Donald Walker.

ASSISTANT: Hello, how may I assist you today?

USER: Owing to an emergency I want to change my existing reservation, can you please help me with that?

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

USER: Sure, take your own time.

ASSISTANT: Thanks for waiting, we have not found any flight reservation on your given name.

USER: Ok, no issues. Thanks for your information.

ASSISTANT: Thank you for choosing us,have a great day ahead.