You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, can I help you?

USER: Yes, I want to change my existing reservation because my health in not good to travel. Can you help me with this?

ASSISTANT: Oh!. Sure, I will help you. With which name you have reserved your existing  reservation?

USER: Shirley Roberts.

ASSISTANT: Sorry Roberts, I didn't found any reservation with your name in our database.

USER: Ok, not an issue.

ASSISTANT: So, I can't change your reservation.

USER: Thank you for your information.

ASSISTANT: Do you need any other help?

USER: No.

ASSISTANT: Ok, thank you for contacting our services. Hope you will reach us in the future.