Ecclesia de mysterio, Article 8 §2:[The function of the extraordinary minister of Holy Communion] is supplementary and extraordinary and must be exercised in accordance with the norm of law. It is thus useful for the diocesan bishop to issue particular norms concerning extraordinary ministers of Holy Communion which, in complete harmony with the universal law of the Church, should regulate the exercise of this function in his diocese. Such norms should provide, amongst other things, for matters such as the instruction in eucharistic doctrine of those chosen to be extraordinary ministers of Holy Communion, the meaning of the service they provide, the rubrics to be observed, the reverence to be shown for such an august Sacrament and instruction concerning the discipline on admission to Holy Communion.
Extraordinary Ministers of Holy Communion at Mass (USCCB):Extraordinary Ministers of Holy Communion should receive sufficient spiritual, theological, and practical preparation to fulfill their role with knowledge and reverence. In all matters they should follow the guidance of the diocesan bishop (Norms for the Distribution and Reception of Holy Communion Under Both Kinds for the Dioceses of the United States of America, NDRHC, no. 28).
There is an Order for the Commissioning of Extraordinary Ministers of Holy Communion.