First of all, don’t be afraid. Second, do not attempt to expel it. The important thing is to turn your attention to Christ.
The simplest way to do this is by making the sign of the Cross.
Elder Porphyrios says,
The most important weapon to use against the devil is the Holy Cross, of which he is terrified. … communication with the Christ, when it takes place simply and naturally without force, makes the devil flee.Also as you make your Cross say the words “Lord Jesus Christ, have mercy on me.’
The Elder says,
This is our method. We will raise our ams to Christ and He will give us grace.This the same approach as given to us by Saint Neilos the Ascetic.
Whenever a temptation comes to you, or a dispute excites you, either to express at once anger towards your adversary or to utter a senseless cry, remember prayer and the judgment concerning it, and at once the disorderly movement in you will subside. (The Philokalia vol 2, trans. Constantine Cavarnos, p65)What we are doing is showing contempt for evil.
Reference: Wounded By Love, p 149 -151