You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I help you?

USER: I am Andrew Williams. Due to my health problem I want change my reservation, can you please help me to change my reservation?

ASSISTANT: Please wait for a moment.

USER: Ok.

ASSISTANT: Sorry, there is no reservation matching with your name in our portal to make changes further.

USER: Ok, no problem. Thank you.

ASSISTANT: Thank you for reaching us.