You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Gregory Martin.

ASSISTANT: How may I help you?

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

ASSISTANT: Ok, please wait a minute.

USER: Sure.

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

USER: That's fine, thank you for your service.

ASSISTANT: Most welcome.