You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I help you at present?

USER: I am Charles Collins, I want to change my reservation due to sudden bad health condition.

ASSISTANT: Sure, I change your reservation right now. Please wait for a while.

USER: Sure.

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

USER: Ok, thank you for informing me.

ASSISTANT: Thank you for approaching our service.