You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: Helen Thomas here.

ASSISTANT: How may I help you?

USER: Suddenly, my friends changed the trip plan.So I want to change the reservation. Can you please help me for that?

ASSISTANT: Sure, wait for a minute.

USER: Ok.

ASSISTANT: Sorry Helen, no reservation found on your name.

USER: Ok, thank you for the information.

ASSISTANT: Thank you for contacting us.