Question:How should a Christian handle sins that have been committed in the past as far as contacting each person whom he has sinned against. Must each person be contacted before the Christian is forgiven?
A similar question was asked a few years ago. See: "In order to repent, do you need to find the people to whom you set a bad example?"
Repentance is the change in a person's behavior because they were sorry for what they had done in the past. "For godly sorrow produces repentance leading to salvation, not to be regretted; but the sorrow of the world produces death. For observe this very thing, that you sorrowed in a godly manner: What diligence it produced in you, what clearing of yourselves, what indignation, what fear, what vehement desire, what zeal, what vindication! In all things you proved yourselves to be clear in this matter" (II Corinthians 7:10-11). Repentance should leave those who know you amazed at how much you have changed for the better.
But as I pointed out in the earlier answer, the past can't be undone. If you know someone has something against you because of your past behavior, you ought to attempt to apologize and make it right. "Therefore if you bring your gift to the altar, and there remember that your brother has something against you, leave your gift there before the altar, and go your way. First be reconciled to your brother, and then come and offer your gift" (Matthew 5:23-24). It won't be possible in every case. Some people won't wish to let go over their hatred, and many you won't know what happened to them over the years. Instead of setting an impossible task for yourself, just plan that if you do happen to run into them again that you will let them know that you were wrong. And by that time they will know you mean it because they will see how much you have changed.
But to directly answer your question, I don't know of any passage that requires a person to track down every person he ever sinned against and apologize before God would forgive them of his sins. Instead, think of it in terms of repentance. If I stole money from a friend, can I claim to have changed while keeping the money? If I had a child out of wedlock, can I claim to have repented while ignoring the child's existence?