Just to redact the fantastic comments of DoubleAA and of Danny Schoemann into a consolidated answer format:
There are the general steps of repentance, namely:
1) Regret that he did it.
2) Stop doing it.
3) Ask forgiveness from anyone harmed (if applicable).
4) Confess to God (Vidui).
5) Accept never to do it again.
(All that done seriously, not just lip-service.)
The Talmud says that if one can't identify the victims of one's theft (or fraud, I assume), then one should give to public-benefit projects, as that way there's a chance that some victims will benefit. (It should be something that helps everyone, not just the poor, unless the victims were all poor.) Maybe the library, volunteer fire department, or the like in whatever towns there are likely to be victims, or if you have no idea, your own town?