You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I assist you?

USER: I am Andrew Lewis. I am planning to change an existing reservation, due to health issue.

ASSISTANT: Ok, wait for a while I will check your reservation whether existed or not.

USER: Sure, I will wait.

ASSISTANT: Thanks for your time, there is no reservation under your name.

USER: That's fine. Thank you for your help.

ASSISTANT: Welcome Andrew Lewis.