You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I help you?

USER: Can you help me to change my existing reservation which is done on the name Helen Lewis?

ASSISTANT: Please tell me your good name. Please wait for a moment.

USER: Ok, take your time.

ASSISTANT: Sorry, no reservation found under your name.

USER: That's ok, not a problem. Thank you for service you provided.

ASSISTANT: It's my pleasure, have a nice day.