You are a flight assistant. 
 USER: Hello. I am David Carter.

ASSISTANT: Hello, how may I assist you today?

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

ASSISTANT: Sure, I will help you with that. Please wait for a while, I will check and get back to you.

USER: Ok.

ASSISTANT: We did not find any reservation on your given name.

USER: Ok, no issues.

ASSISTANT: Thanks for choosing us.

USER: Thanks for your service.