You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How can I help you?

USER: Alexander Campbell here. Due to my health issues I would like to change my recent reservation, which I have done last week. Can you help me to change my existing reservation?

ASSISTANT: Ok. Sorry, there is no reservation found by your name.

USER: It's ok, maybe it was not properly while booking. Anyway, thanks for checking.

ASSISTANT: Thank you and have a nice day.