How can I return stolen rights to their owners, knowing that I only know one of them and do not know the others or their number?

The questioner must initiate a sincere repentance from every sin. Part of complete repentance is to return rights to their owners as much as possible. If he cannot identify the owners of the rights or inform them, he must give in charity the equivalent amount of the stolen money on their behalf, for Allah, the Almighty, says: "Allah does not burden a soul beyond its capacity."