You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello,.

USER: I am Brandon Williams.

ASSISTANT: How can I render you today?

USER: I want to change an exesting reservation due to sudden change in my trip.

ASSISTANT: Ok.

USER: Can you help me?

ASSISTANT: Sure, we are here to aid you. Sorry Williams, there is no active reservation found on your name.

USER: No issue. Thank you.

ASSISTANT: Thank you for availing us.