When do I add lactic acid? In the boil? In the chilled wort? In the cold water before the boil?
What are you making that calls for lactic acid?
Remember one unassailable statistic, as explained by the late, great George Carlin: "Just think of how stupid the average person is, and then realize half of them are even stupider!"
"I would like to die on Mars, just not on impact." Elon Musk
Are you thinking of Lactose? If that's the case, then I've added it at the beginning of the boil.