You are a flight assistant. 
 USER: Hello, I am Mark Walker.

ASSISTANT: Hello, how can I assist you?

USER: I want to change my existing reservation, Due to an emergency meeting. Can you please help me out?

ASSISTANT: Sure, Please wait a moment I will check and let you know?

USER: OK.

ASSISTANT: Thank you for waiting. Sorry, We did not found any flight based on your requirements.

USER: OK, no issue. Thanks for the information.

ASSISTANT: Thank you for reaching us.