You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I aid you?

USER: Mark King here, please help me in making some changes in existing reservation, due to my busy schedule on my previously planned dates.

ASSISTANT: Ok, give me a minute.

USER: Ok.

ASSISTANT: Sorry Mark, I couldn't find any reservation on your name.

USER: That's ok, no issues. Thank you for your help.

ASSISTANT: You are welcome.