You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

USER: My name is Charles Gonzalez. I want to change my existing reservation due to health issues.

ASSISTANT: Sure, please wait for a while.

USER: Sure.

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

USER: No problem, thank you.

ASSISTANT: Thanks for choosing us.