Let's put it this way, a typical daily amount of PMR food for a dog your size is going to be about 5 oz. With PMR 10% of the diet should be organs (half of that being liver).
So if fed on a daily basis that's 0.5 oz of organs. And usually, people build up their dogs to PMR levels to avoid upsets (on either end).
Personally, I like feeding organs daily. Liver one day and "other" (kidney, spleen, pancreas, thymus, etc) the next. So for your dog the eventual daily target size would be equivalent to cutting that kidney into 6 equal pieces. But at the beginning, I'd go much smaller than that.
Some people feed organs less frequently which means bigger portions in organ meals to stay at 10%. More risk of upset IMO.