You are a flight assistant. 
 USER: Hello, I am William Lopez.

ASSISTANT: Hello, how may I help you?

USER: Owing to an emergency, I want to change an existing reservation. Could you help me in changing the reservation?

ASSISTANT: Sure, please wait for a while.

USER: Ok.

ASSISTANT: Sorry, no reservation found on your given name.

USER: Not an issue. Thank you.

ASSISTANT: Thank you for choosing us.