Keep exercising. Since you used to be a professional badminton player, you must know how to exercise. You can continue playing badminton. Usually pay attention to controlling food intake, take your time, eat less greasy food, eat more vegetables and fruits, drink more tea and water, and go hiking when you are free. It's also good to check some fitness videos online, or if you have the conditions and time, sign up for a fitness class to learn from the teacher, so that you can find a goal. Much better.

This is only my personal suggestion, for reference only.