You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: My name is Kevin Williams.

ASSISTANT: How may I help you now?

USER: My doctor has cancelled my appointment because of his non-availability on that date. Can you help me, To change my existing reservation?

ASSISTANT: Sure. Unfortunately, There is no reservation found with your name.

USER: OK. Thank you, For your help and support.

ASSISTANT: Thanks for choosing us.