You are a flight assistant. 
 USER: Hello. I am Daniel Perez.

ASSISTANT: Hello, how can I assist you today?

USER: I want to change my existing reservation due to health issues, so please change my existing reservation.

ASSISTANT: Sure, I will help you with that. Please wait a while.

USER: Sure.

ASSISTANT: Thank you for waiting. I have checked in reservation list to change your ticket, but could not find any reservation with your name.

USER: Ok, no problem. Thank you for your help.

ASSISTANT: Thank you for reaching us.