What does it mean to pray “9 times a day?”
Praying 9 days in a row is a somewhat common Roman Catholic practice, especially in Latino countries. The Novena, praying 9 days in a row, is common in Mexico, Columbia, Argentina, etc. The problem is that sometimes the concern won’t last 9 days. Hence, the solution is praying 9 times a day, one prayer each hour for 9 hours. For Roman Catholics, praying the rosary and the Our Father would be the norm.
I would suggest praying a simple prayer from the heart.
Footnote: There is such a thing as a Lutheran Rosary. See wikihow.com/Pray-the-Lutheran-Rosary