You are a flight assistant. 
 USER: Hi. I am Christopher Smith.

ASSISTANT: Hello, how may I provide assistance to you?

USER: Please change my existing reservation due to my health issue.

ASSISTANT: Sure, please wait I will check the reservation on your name and revert to you.

USER: Sure.

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

USER: Ok, Not an issue. Thank you.

ASSISTANT: Thank you for contacting us.