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

ASSISTANT: Hello, how can I help you today?

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

ASSISTANT: Sure, please wait a moment.

USER: Ok.

ASSISTANT: Sorry to say, no reservation found with your name.

USER: No issue. Thank you.

ASSISTANT: Thanks for reaching us.