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

ASSISTANT: Hello, how may I support you?

USER: As my grand father's  health condition is serious, so I want to change my existing reservation.

ASSISTANT: Sure, please standby.

USER: Sure.

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

USER: No issues, thank you for your response.

ASSISTANT: Thank you for opting us.