You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I aid you today?

USER: I am William Allen. I want to change my existing reservation due to health issues.

ASSISTANT: Sure, we are here to help you to change your reservation. Please wait for while.

USER: Sure.

ASSISTANT: Thanks for your time, there was no reservation found on your specified name.

USER: No problem, thank you for your service.

ASSISTANT: Thank you for choosing us.