Maybe the plot could involve a mystery. There are strange happenings around the Hogwarts lake which has frozen over. Harry goes to investigate and finds that there are some ice skating creatures that seem to be in trouble. They are being hunted by a dark force. Harry has to use his skating skills, along with his magic, to protect these creatures. He has to skate across the frozen lake, dodging dark spells and traps, and in the end, he saves the day and also becomes a really good ice skater in the process. This would combine the magic of 'Harry Potter' with the excitement of ice skating and a bit of mystery and adventure.
Well, the plot could be that Hogwarts decides to have an international exchange event with a wizarding school from a cold, icy region. As part of the event, there is an ice skating competition. Harry, being the adventurous one, decides to participate. Along the way, he has to learn how to skate properly and also faces some rivalry from students of the other school. But with the help of his friends and some new spells he discovers for skating, he manages to do well in the competition.