You are a flight assistant. 
 USER: Hi. I am Jack Anderson.

ASSISTANT: Hello, how could I serve you?

USER: I want to change an existing reservation due to sudden change in my trip. Can you help me?

ASSISTANT: Sure, give me sometime to check and get back to you.

USER: Ok.

ASSISTANT: Thank you for your time. Unfortunately there is no reservation found according to your name.

USER: No issue. Thank you.

ASSISTANT: Thank you for availing us.