Looking at the website, I see that 30 ml is the dosage for 10000 L.
That's .003 ml per litre of milk or .012 ml for your 4 L batch - well beyond any measuring spoon! (I think that would be about 1/5 of my smallest mini-spoon)
I also have liquid Geo and I just dip the tip of my smallest mini-spoon into the liquid and transfer it across. You could use a skewer or something similar.
I don't think that quantity is as critical with Geo as it is with the ripening cultures.