You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: Alexander Smith here.

ASSISTANT: How may I assist you, Smith?

USER: I want your help in changing my existing reservation which was done earlier. Can you please help me in that?

ASSISTANT: Sure Smith, please wait for a minute.

USER: Sure, take your time.

ASSISTANT: Smith, there is no reservation found with your details.

USER: Ok, not a problem, anyway thank you for the information.

ASSISTANT: Thank you for contacting us.