What should I do if the former business owner wants to recruit again after two years' resignation?

I read your question, and I personally suggest that you don't go back. Since he can't find anyone, you can take his place. The most important thing in the market now is people. It will happen again. If he finds someone more suitable than you, he will eliminate you in the same way. If you go back, he may think you are low (sorry for my improper use of words), and he will not cherish you very much. These are just our suggestions. It's up to you. If it were me, I wouldn't go back. Make him regret it. Have the ability not to be afraid of not finding a job, and believe that you are the best.