There are many Santa Muerte prayer, one of my favorites is this one.
Jesus Christ the conqueror, who on the cross was conquered.
Conquer (name of person), that he be conquered with me in the name of the Lord.
If you are a fierce animal tame as a lamb, tame as the flower of rosemary, you must come.
You ate bread, and of it you gave to me, and by the strongest word that you gave me, I want you to bring me (name of person).
That he be humbled, defeated at my feet to complete what he has offered me.
Santisima Muerte, I beseech you lovingly inasmuch as Immortal God formed you with your great power over all mortals.
So that you might place them in the celestial sphere where we may enjoy a glorious day without night for all eternity.
And in the name of the Father, the Son and the Holy Spirit, I pray and I beseech you that you deign to be my protectress.
And that you concede all the favors that I ask of you...
Until the last day, hour and moment in which your Divine Majesty commands to take me before your presence. AMEN.