You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: This is Alexander Miller.

ASSISTANT: How may. How may I help you?

USER: Could you please help me to change my existing reservation?

ASSISTANT: Yes definitely. Wait a minute.

USER: OK.

ASSISTANT: Sorry! no reservation I found with your name.

USER: OK, thank you for the information.

ASSISTANT: Most welcome.