Read the wiki article on conditions to fully understand how to address the objects you want.
The basic way events work is to pick an object you want to affect (or as you put it, address) by using conditions. For example, any SpriteA actions in a 'mouse is over SpriteA' event will only affect the SpriteAs under the mouse. If you want to affect just one object, you need to think of the condition or conditions that will pick just that instance. It's a different way of thinking compared to scripting or programming languages - first isolate the instances with conditions, then do something to them - but it becomes natural with some practice.