The Catholic Church does not in anyway allow just anyone to become an exorcist. In fact, there is a exact set of qualifications that must be met before admitting anyone into this harrowing ministry.
The number one requirement is the priesthood. But even at that , according to the Roman Ritual, only certain priests can become exorcists.
A priest who is expressly and particularly authorized by the local Bishop. And when he intends to perform an exorcism over persons tormented by the devil, he must be properly distinguished for his piety, prudence, and integrity of life. He should fulfill his devout undertaking in all constancy and humility, being utterly immune to any striving for human aggrandizement, and he should, not on his own, but on the divine power.
The exorcist should not believe immediately that a person is possessed by an evil spirit; because he ought to ascertain the signs by which a person possessed can be distinguished from one who is suffering from some illness, especially one of a psychological nature.
In that case, priests who become exorcists are holy men who do not seek out this ministry for power or self-gain, but are called by God for this specific task. It takes some years of careful study before a priest is properly prepared for such a task and the ministry is not taken lightly.
Under no circumstances should a lay person permitted to become an exorcist, though laypeople can “assist” an exorcist on some special occasions. Same rules apply to these assistants too. They should have a devout prayer life and united to the sacraments. They need to be properly prepared for such an experience, because a person attached to sin could severely hamper the exorcism process.
The devil will try with all of his might to further his influence during an exorcism, and so anyone involved with casting out a demon must rely entirely on the power of God to protect them.
It’s a spiritually dangerous vocation, one that requires a great deal of holiness and humility.