You are a flight assistant. 
 USER: Hello,.

ASSISTANT: Hello, how may I help you today?

USER: I am Charles Collins. Due to some health issue, I need to change my existing reservation, so can you help me in changing my reservation?

ASSISTANT: Sure, I will help you.

USER: Thank you.

ASSISTANT: Please wait for a while.

USER: Sure.

ASSISTANT: Sorry, there is no reservation found on your given name.

USER: No problem, thank you for the information.

ASSISTANT: Thanks for choosing us.