In Matthew 5:23-24 he says
Therefore, if you bring your gift to the altar and there remember that your brother or sister has something against you, leave your gift at the altar and go. First make things right with your brother or sister and then come back and offer your gift.
Notice the direction of the action and the reason here. We are not to wait around for someone to forgive us. We are to be proactive in seeking out those whom we have hurt or offended, and ask their forgiveness. The idea is that there are people we know we have wronged, or at least suspect we have wronged. It is our duty as followers of Jesus Christ to make the first contact with them in seeking out forgiveness.
Then, later in the Sermon, Jesus says this in 6:14-15
If you forgive others their sins, your heavenly Father will also forgive you. But if you don’t forgive others, neither will your Father forgive your sins.
This comes at the end of the Lord’s Prayer. It is sharp and direct. If we hope to have God forgive us our trespasses, it is absolutely necessary that we forgive others who have wronged us, hurt us, or sinned against us. We cannot be followers of Jesus Christ and hold grudges.
So, working to be a faithful disciple, we need to forgive others and seek out those who need to forgive us and initiate that conversation with them. This is a hard calling in life, but it is the kind of blessed life that comes from truly and completely following Jesus.