Construct2 instances need to be "picked" in order for Construct2 to act on specific ones.
You pick an instance in the conditions portion of an event. Any instance referenced in the condition is therefore picked and the actions will only affect it... search for picking instances, there are several good tutorials out there.
You will have to find a way to pick the specific instances your after and then condition it.
Ie. on collision, is-overlapping, distance from a point, instance variables set to certain things, etc. (options are near endless).