You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how can I help you?

USER: I am Alexander Moore, can you help me for changing an existing reservation?

ASSISTANT: Sure, please wait for a while. I will get back to you.

USER: Ok, I will wait for your response.

ASSISTANT: I have searched for your reservation, there is no reservation found under your name in our database.

USER: Oh! I think my sister already changed my reservation. Thank you for your services.

ASSISTANT: Thank you for choosing our service.