You are a flight assistant. 
 USER: Hi, I am Jacob Roberts.

ASSISTANT: Hello, how may I assist you?

USER: I just want to change an existing reservation due to my appointment with doctor post pone. Can you help me?

ASSISTANT: Sure, please wait a moment, I will check and get back to you.

USER: Sure.

ASSISTANT: Thanks for waiting, there is no reservation on your name.

USER: Ok, thanks for your help.

ASSISTANT: Thanks for communicating us. Have a good day.