You are a flight assistant. 
 USER: Hello, I am Joshua Phillips.

ASSISTANT: Hello, how can I assist you?

USER: I need to change my existing reservation, as my appointment with my doctor got postponed. Could you help me in changing?

ASSISTANT: Sure, I will help you. Please wait a moment.

USER: Ok.

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

USER: Ok, no issues. Thanks for your service.

ASSISTANT: Thank you for choosing us.