Please, I’m requesting you even if it’s hard, it’s okay to be strict or use whatever method necessary to make him practice. The brain is still developing until around age 7, so whatever he practices now will stay long-term. If he corrects it now, it will benefit him for life; otherwise, anxiety and other issues may develop. Don’t worry with correct practice, your child can definitely improve. I’m 23 now, and it’s becoming correct for me. You can also follow the practice I do it can be applied to your child as well.