They should call for the elders of the church and have them pray over them, anointing them with oil in the name of the Lord. Pray for one another, pray for forgiveness, pray for backsliders, pray, pray, pray. It's that simple - a church is a house of prayer. That's what it means to be a church. We are called to be a house of prayer, like we have been for 167 years.
Churches sometimes forget that.
Somewhere through the years prayer loses it's focus. Prayer loses it's central place. As the years go by we can get distracted by all the busywork and forget how to be a house of prayer. A very expensive consultant was called in to help a congregation which was in deep conflict. They just could not get along with a preacher.