Do NOT lay hands on the possessed person, except as necessary to prevent bodily harm. Stay close to the new convert and help him get involved in a solid program of discipleship in fellowship with other believers. It is extremely important to understand that believers in Jesus Christ can be oppressed, but not possessed by demons. God will not share His temple with Satan. Greater is He that is within you, than he that is within the world.
Christians can do things that open the door to demon oppression.
This happens when one strays from obedience to the Lord Jesus Christ. If a Christian insists upon constantly sinning, Satan can, and will take the opportunity to oppress him further, and try to drive him away from God.