Recite the Consecration Prayer to the Sacred Heart of Jesus, an expiatory prayer ordered by Pope Pius XI

“At length, in the year 1765, the Supreme Pontiff Clement XIII approved the Mass and Office in honour of the most Sacred Heart of Jesus; and Pius IX extended the feast to the universal Church. From then on the worship of the most Sacred Heart, like an overflowing river, washing away all obstacles, hath poured itself forth over all the earth, and, at the dawn of the new century, Leo XIII, having proclaimed a jubilee, decided to dedicate the whole human race to the most Sacred Heart. This consecration was actually carried out with solemn rites in all the churches of the Catholic world, and brought about a great increase of this devotion, leading not only nations but even private families to it, who in countless numbers dedicated themselves to the Divine Heart, and submitted themselves to its royal sway. Lastly, the Sovereign Pontiff Pius XI, in order that, by its solemnity, the feast might answer more fully to the greatly widespread devotion of the Christian people, raised the feast of the most Sacred Heart of Jesus to the rite of a double of the first class, with an octave; and moreover, that the violated rights of Christ, the supreme King and most loving Lord, might be repaired, and that the sins of the nations might be bewailed, he ordered that annually, on that same feast-day, there should be recited an expiatory form of prayer in all the churches of the Christian world.“

 - Breviarium Romanum