Please explain this in details and any relevant theories , step by step explanations, thank you.

The diagrams below show the supply and demand of the perfectly competitive market for Thai rice and the cost curves of an individual rice farmer. There is a fall in demand for Thai rice as Singaporean rice is deemed healthier. What action should the rice farmer take in response to the change in demand? Explain, is the action the optimal [e.g. minimizes the loss]