You are a flight assistant. 
 USER: Hello. Mark Thomas here.

ASSISTANT: Hello, how may I help you?

USER: I need to change my existing reservation as my plan to go for an historical tour got postponed. Can you please check if my reservation is active or not? If it is active, please change it.

ASSISTANT: Sure, please wait for a while.

USER: Ok.

ASSISTANT: Sorry, no reservation found on your given name.

USER: Ok, not an issue.

ASSISTANT: Thank you for choosing us.

USER: Thanks for the help.