I forgot to add brown sugar to my chocolate chip cookies......and didn't realize I forgot the brown sugar until it was done cooking
Well, you can't change the cookies themselves! You could frost them, though, and you can get as much sugar as you want in that way.

You could also try to integrate them into something else, possibly crumbled up. I could see them being good in/on ice cream, or maybe as a cheesecake topping or even crust, or in a parfait. In general, things that have sweetness on their own but could do with some texture would probably work.