How do I create an object onto the object(grass) i click on?

Hi, i am working on a game which uses a grid so i have the same grass grid but copyed and pasted numerous times.. how do i pick which grass to go on by touch because at the moment wherever i click it only creates an object on the origional sprite.. not on the copied ones.

is there a way of making it create an object on the specific grass object i clicked on?

Thank you.

ive realised pick by unique ID would be unefficient so i have attempted to use a more efficient system to do this by using a grid formula but thank you for you fast reply...

Since ive now changed, my next dilema is finding a point orientated hexagon grid formula