You are a flight assistant. 
 USER: Hello. I am Timothy Roberts.

ASSISTANT: Hello. How may I guide you today?

USER: I am planning to change an existing  reservation, due to health issue. Can you please change my reservation?

ASSISTANT: Sure, I will help you with that. Please wait for a while.

USER: Sure, take your own time.

ASSISTANT: I am sorry to say that there is no reservation found.

USER: That's ok. Anyways, thank you for your help.

ASSISTANT: Thank you for contacting us.