You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How may I help you?

USER: I want to change my existing reservation which is done recently due to some health issues, can you please help me in this?

ASSISTANT: Sure, I will help you with that. Can you please tell me your name?

USER: Sure, my name is Thomas Hill.

ASSISTANT: I regret to tell you that, there is no active reservation found in our portal to change the ticket details.

USER: Ok, not an issue. I will try with another booking agency.

ASSISTANT: You are welcome. Thank you for opting us.

USER: Anyways, thank you for your service.

ASSISTANT: You are welcome.