Who changed the oil and why did he open the chamber? Just open the drain bolt and let the oil drain out, measure the quantity that came out and put the same quantity back in. Simple. Why complicate things. And the guy who did the change should have checked the oil level on the dip stick before changing the oil. Now there's no way of telling how much oil came out and how much needed to be put in.
Now the right thing to do is to follow the dipstick and drain the excess oil.