In Construct, you need to understand the concept of "Picking".
Picking is used to specify which instance of the object you want to apply your action to.
If you apply your action without Picking an object first, the action will be applied to ALL instances of this object.
For example, check this simple code:
Here, we did not Pick any instances. So ALL the Sprite objects will have their Variable1 value set to 166556.
But what if we want only ONE Sprite to have its value set to 166556, while the rest of the Sprite objects remain the same?
Here we need to use a Picking condition; which will tell Construct which one of these Sprite objects we want to change.
Notice we added a new condition that starts with "Pick". You can find these conditions under the System plugin, under a category named "Pick instances".
There are different types of Picking, each one is useful in a specific situation. You can check the manual for detailed explanation. But in general, each one offers you a different way to specify objects.
Additionally, some objects offer you additional ways to Pick instances:
One important thing to keep in mind when Picking instances, is that once you pick something, all the sub-events, sub-actions, and sub-conditions will only focus on the picked instance.
You can think of Picking as a "Filter". It filters instances of the object so you can only focus on a specific group of them.
For example, if you have 100 Trash Cans, and you want to do something for the Cans in the lower left corner of the map. Then you can filter the instances (using Picking!) to only choose the ones with X and Y within the lower left corner area.
Additionally, you can apply multiple filters. So you can Pick a group of objects, then add a sub-condition and add another filter. Now the first filter will be applied to ALL instances. Then the second filter will be applied to the RESULT of the first filter.
So if you have 100 Trash Cans, and the first filter picked 10 out of them, then the second filter will choose from the 10, NOT the 100.
So for your specific case, I understood from earlier replies that one part of your project is applying an action to ALL instances of the object. So, you can probably guess by now that you need to -somehow!- Pick the specific instance you need to change.
In the end, Picking can be considered an advanced feature, and it really caused me confusion many times during my time with Construct! But once you experiment with it, you will find out that it gives you some quite powerful tools to control your game!
Good Luck!