In the book of Matthew Jesus instructs us
Vs 15-20
15"If your brother sins against you,[b] go and show him his fault, just between the two of you. If he listens to you, you have won your brother over. 16But if he will not listen, take one or two others along, so that 'every matter may be established by the testimony of two or three witnesses.'[c] 17If he refuses to listen to them, tell it to the church; and if he refuses to listen even to the church, treat him as you would a pagan or a tax collector.

18"I tell you the truth, whatever you bind on earth will be[d]bound in heaven, and whatever you loose on earth will be[e] loosed in heaven.

19"Again, I tell you that if two of you on earth agree about anything you ask for, it will be done for you by my Father in heaven. 20For where two or three come together in my name, there am I with them."