You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I amend you?

USER: Can you change my existing reservation by the name John Mitchell?

ASSISTANT: Sure, give me a moment to check and let you know.

USER: Sure.

ASSISTANT: Unfortunately, there is no reservation exist on your name to change.

USER: Ok, No issues. Thank you.

ASSISTANT: Thank you for choosing us.