If you need to take time off for evening self-study on your birthday, you can apply to the class or school counselor or teacher. You can write a leave letter stating that your birthday is the same day. I hope you can take time off to celebrate. In the letter, you can express your gratitude to the school and teachers, and promise that you will try your best to make up the missed courses in the future. The leave letter should be given to the counselor or teacher enough time in advance so that they can arrange your leave application and inform your classmates.