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

ASSISTANT: Hello,. How can I serve you?

USER: Owing an emergence, I need to consultant my doctor so I need to change my existing reservation.

ASSISTANT: OK, please wait a moment I will get back to you?

USER: OK.

ASSISTANT: Sorry, I have not found any reservation in your name.

USER: OK, no issue.

ASSISTANT: Thank you, for choosing us .