I’m an atheist so I have a natural immunity against being possessed by evil spirits or demons but this might be helpful for religious folks who need to perform an exorcism.
I adjure you, ancient serpent, by the judge of the living and the dead, by your Creator, by the Creator of the whole universe, by Him who has the power to consign you to hell, to depart forthwith in fear, along with your savage minions, from this servant of God, N., who seeks refuge in the fold of the Church. I adjure you again, X (on the brow) not by my weakness but by the might of the Holy Spirit, to depart from this servant of God, N. , whom almighty God has made in His image.
