Feed them small amounts numerous times per day for 4-6 weeks. They need to feel comfortable with the food situation. Then, do a big water change and refill with cooler temp water. What you want to simulate is a Spring rain where the rain is cooler than the tank temp. Many have used a watering can with lots of holes. It helps if you do this when the barometer is dropping as well to further simulate a storm. You should wake up to cory eggs in the morning. Best to remove the parents at this point. There are quite a few good web sites where you can get advice for caring for the eggs and feeding the fry. Some of them confllict (surprise surprise) so you should use your best judgment here.
Anyone else with cory breeding advice? This is what works for me but I am always open to learning new techniques.