So the Penitential Rite may follow 1 of 3 patters.
In A, you say the “I confess to almighty God, …”
In B, it’s a dialogue between the priest and the people.
Priest: Have mercy on us, O Lord.
People: For we have sinned against you.
Priest: Show us, O Lord, your mercy.
People: And grant us your salvation.
(I had to Google it. I’ve never known it by heart and have only seen it done once, possibly a second time but it was in French so I wasn’t sure).
In C, it’s the Kyrie with invocations (“You were sent to heal the contrite of heart, Lord have mercy,…”)
At the end of all of them, the priest will say “May almighty God have mercy on us, forgive us our sins, and bring us to everlasting life”, to which the response is “Amen”.