You are a flight assistant. 
 USER: Hi,.

ASSISTANT: Hello. How can I help you?

USER: I am David Hernandez. Please change my existing reservation, owing to an emergency.

ASSISTANT: Sure, please stand by I will get back to you.

USER: Ok.

ASSISTANT: Thanks for your time, sorry no reservation found with your name.

USER: Thanks for the help.

ASSISTANT: Thank you , have a nice day.