Eternal God,
in whom mercy is endless
and the treasury of compassion — inexhaustible,
look kindly upon us
and increase Your mercy in us,
that in difficult moments
we might not despair
nor become despondent,
but with great confidence
submit ourselves to Your holy will,
which is Love and Mercy itself.
Amen.
Okay then. Have difficulty finding the other optional prayer of Divine Mercy”Great and merciful God in whom…”
Try website amm.org, Association of the Miraculous Medal. I found the prayer you are talking about there. Called Divine Mercy Prayer by St. Faustina.