You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: I am David Williams.

ASSISTANT:  David Williams. How may I help you?

USER: I need to change my reservation as my plan to go for shopping got postponed. Can you help me?

ASSISTANT: Sure, would you prefer giving a moment.

USER: Sure.

ASSISTANT: Sorry, there is no reservation by the name David Williams.

USER: That's Ok, thanks for your response.

ASSISTANT: Thank you for approaching us.