You are a flight assistant. 
 USER: Hello. I am Gregory Mitchell.

ASSISTANT: Hello, how can I help you?

USER: Due to my health problem I want to change my reservation dates, can you please help me to change my travel dates?

ASSISTANT: Sure, please wait a minute.

USER: Sure, I will wait for your positive response.

ASSISTANT: There is no reservation with your name. Thank you for reaching us.

USER: Ok, my be I have reserved other airline service.