How to know the exact day you ovulate

Jess
Does anyone use Ovia and FF as well that can help me? On Ovia there's a button to actually click when you ovulate but how do you know which day exactly that is? I took opk and put in the days they were positive. When do you ladies put that you ovulated?
Also with FF I know it automatically puts the cover line on your chart but I don't even have the vertical solid red line. When will that show?