I played a round with my friend and we approached short par 3 with the green on the hill separated by the water from the tee. His first shot went left to the green and he thought it was OB. He decided to play provisional but that shot went to the water. Then he decided to use the drop point closer to the green. On the way to that drop point we spotted the first ball somehow in the play. He then decided to play first ball. Can he do that and if yes, how would he calculate his next shot ?