You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Donald Walker.

ASSISTANT: How can I assist you at this moment?

USER: I just want to change my existing reservation, due to some personal problem, can you help with it?

ASSISTANT: Sure, I will help you with this. Please give me a moment to check your reservation status.

USER: Sure, take your own time.

ASSISTANT: Donald Walker, there is no active reservation found under your name in our database.

USER: Ok, no problem. Not an issue.

ASSISTANT: Thank you for contacting us.

USER: Thanks for your help.