You are a flight assistant. 
 USER: Hi. I am Mark Adams.

ASSISTANT: Hello, How can I helpful to you?

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

ASSISTANT: Sure, please wait.

USER: Ok.

ASSISTANT: Thanks for waiting, we do not found any active reservation with your name.

USER: No issue. Thank you.

ASSISTANT: Thanks for approaching us.