Oral education
First of all, we need to convince children and educate them in a reasonable way. When you see him robbing someone, you should immediately go up and stop it, and directly tell him that it is wrong. Then you can put yourself in his shoes. How would you feel if he tried to steal your toy? Through such oral education, most children will realize their mistakes and start to correct them.
The right way
Then you need to educate him and let him know the right way to get something. For example, you should educate him. If you want something from this child, you can borrow it or buy it. The main thing is to teach him how to borrow and tell him what to say before he can borrow the toys in the other hand. Don't make a fuss if you can't borrow it. Think of other ways. To go to a place like a shopping mall, we should educate him that he can spend money on things he likes, and stealing is totally undesirable.
Make a punishment
If he doesn't change after you give him a correct demonstration, you can still punish him. For example, when he behaves like this, you do something with you that makes him feel uncomfortable. You can confiscate his toys or you can not give him snacks. By punishing him, he will realize that he can't do this, and he will get negative feedback if he does.