"If another believer sins against you, go privately and point out the fault. If the other person listens and confesses it, you have won that person back.
References for Matthew 18:15
But if you are unsuccessful, take one or two others with you and go back again, so that everything you say may be confirmed by two or three witnesses.
If that person still refuses to listen, take your case to the church. If the church decides you are right, but the other person won't accept it, treat that person as a pagan or a corrupt tax collector.
I tell you this: Whatever you prohibit on earth is prohibited in heaven, and whatever you allow on earth is allowed in heaven.
"I also tell you this: If two of you agree down here on earth concerning anything you ask, my Father in heaven will do it for you.
For where two or three gather together because they are mine, I am there among them."
References for Matthew 18:20
Then Peter came to him and asked, "Lord, how often should I forgive someone who sins against me? Seven times?"
References for Matthew 18:21
"No!" Jesus replied, "seventy times seven!
References for Matthew 18:22