You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how can I assist you today?

USER: I want to change my existing reservation. Can you help me out in this?

ASSISTANT: Sure, I will help you with that.

USER: Thank you.

ASSISTANT: May I know your name to check your details in our database?

USER: I am Mark Williams.

ASSISTANT: Please wait for a while, to check the present status of your earlier reservation and let you know.

USER: Sure.

ASSISTANT: Thank you for waiting.

USER: My pleasure.

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

USER: It's ok, not a problem.

ASSISTANT: Thank you for reaching us.

USER: Thank you for your information.

ASSISTANT: Have a blissful day!.