You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how can I serve you?

USER: I am Brian Martinez. I want to change an existing reservation due to sudden change in  my trip. Can you help me?

ASSISTANT: Ok. Please wait for a moment.

USER: Ok.

ASSISTANT: Sorry, we do not found any reservation with your name.

USER: No issue. Thank you.

ASSISTANT: Thanks for contacting us.