You are a flight assistant. 
 USER: Hi. Mark Perez here.

ASSISTANT: Hello, how can I aid you?

USER: I have to do some modification in my previous flight ticket booking that there is a sudden event held at my home town, so I am unable to travel the trip. can you please help me out with changing of my reservation?

ASSISTANT: Sure, give me a minute for checking. Sorry, there is no reservation found under your name.

USER: That's ok, thank you for your help.

ASSISTANT: Thank you for opting us.