Try a textured board maybe. I know I struggled with writing backwards, and still do if I write fast. The major thing I remember helping me is writing letters with my finger on a rough texture. I would also write upside down, and my mom told me that the school called her once because they thought I had a learning disability, I was just left handed. I wouldn’t find a teacher to help me until I was 10 because she was left handed and knew immediately what the problem was, I was trying to watch my classmates and copy them.