Teacher:In this task, you are given a conversation between a flight agent and the customer. You are given 4 options and you need to select the goal of the conversation. It is provided as part of customer's context, which has to be one of the following: `book`: Make a new reservation, `cancel`: Cancel an existing reservation, `no_flight`: No flight found for the customer's preference, `no_reservation`: No reservation / No change / No cancellation was made in the conversation, mostly enquiring details
Teacher: Now, understand the problem? Solve this instance: customer: Hello. 
 agent: Hello, how may I assist you? 
 customer: I am Christopher Gonzalez. I want to change my existing reservation due to health issues, can you help me in changing the reservation? 
 agent: Sure, we are here to help you. Please give me a moment to check your details in reservation list. 
 customer: Sure. 
 agent: Thank you for waiting, there is no reservation exist on your name to do modification. 
 customer: No problem, thank you. 
 agent: Thank you for contacting us.
Student:
no_reservation