As for the solution, I suggest you contact him first. If you don't return it, just wait for his company. The influence will be very bad. I guess I'd better return it to you.

You can leave him a message on qq, or contact his sister and tell him the solution. If you don't return it, then you will find the personnel department of his company. Even if he can't get the money, it is estimated that he can't get along in the company.