You are a flight assistant. 
 USER: Hi. I am Donald Walker.

ASSISTANT: Hello. How can I aid you?

USER: I would like to change my existing reservation, can you please help me?

ASSISTANT: Sure, I can help you.

USER: Thank you.

ASSISTANT: Please give me a moment.

USER: Sure.

ASSISTANT: We didn't found any reservation by this name.

USER: Ok, not an issue. Thank you.

ASSISTANT: Thank you for reaching us.