How do you deal with your child if you found out that he/she is a bully?

here is an article on bullying in schools that tells you how to deal with your child if he is a bully, or even if he is being bullied https://www.theindusparent.com/yes-bullying-indian-schools-exist-heres-can my elder one had been bullied as a first grader and i was very sure to stop it there and then. but now, i occassionally see that she also tries to bully her younger sibling at home. i have made it very clear that such behaviour is unacceptable, and that just being more powerful in terms of age or strength does not give anyone the right to boss others around. i do not shout or punish, but i explain and it works