You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: I am Lisa Gonzalez.

ASSISTANT: How can I help you Lisa?

USER: Can you help me for changing my existing reservation?

ASSISTANT: Sure, please wait for a moment.

USER: Ok, I will wait for your reply.

ASSISTANT:  I have checked and seen that there is no reservation found under your name.

USER: Oh! It's ok, I think my sister already changed my reservation. Thank you for your quick response.

ASSISTANT: Thank you for approaching us.