How can a seller of tapes, who was robbed a long time ago, be compensated after repentance, knowing that he is no longer in his place and his whereabouts are unknown, and does charity waive his right?

You did well in repenting. As for the music tapes you stole, you are only obliged to guarantee the value of the empty tapes, not what they contained of forbidden music, as that is a waste that is not guaranteed.

If what you gave in charity on behalf of the shop owner is equal to or more than the value of the empty tapes, then you have fulfilled your obligation, because what is forbidden is not to be compensated. If a person despairs of knowing the owners of rights, he should give charity on their behalf.