How do I pick an object by if the mouse is over it?

I am creating a game which is a little bit like a match-3 game (such as candy crush or royal match), however (for now) it uses a mouse. I need the game to know what to do to a specific instance of the sprite to move it, so I am trying to pick that specific instance, but I don't know how. Any ideas?

Thanks in advance!

"Mouse: Cursor is over object" event will pick the object instance. Make sure to configure the collision polygon correctly.