As far as I know, pectin has to be boiled with the sugar to work. I doubt stirring some in later cold will do anything. Runny jam is still wonderful syrup for pancakes, ice cream topping etc.
Fruit jams are often made without pectin, because the fruit has its own. They don't set up/gel as hard as jellies, but should be thicker than syrup, thick enough not to run off your toast. That is accomplished just by boiling it down. It is tricky though getting that just right so it thickens, but doesn't turn in to fruit leather.