You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I guide you today?

USER: My name is Christine Walker.

ASSISTANT: Welcome to flight booking agency Walker.

USER: Due to health issue, I want to change my existing reservation. Please help me in that.

ASSISTANT: Sure, I will help you with that.

USER: Thank you.

ASSISTANT: Please wait a moment to check. We regret to inform you that there is no reservation found on your name in our records.

USER: No problem, thanks for your valid information.

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