You need to get some basic skills in After Effects. It is not a program you can just start using without learning the basics and expect to have any success at all.
Having said that here's what you need to do.
Duplicate Comp 2 in the project panel (not the layer panel) so you have a "Comp 3". Add it as a layer to Comp 1. Now make changes to Comp3 and you will see the difference.
Understand Comp2 is always going to be Comp2 no matter how many times you duplicate it in the layer panel. Every time you make a change to Comp2 that change will be seen in every layer named Comp2 no matter what composition it's nested in. That's what you need to do.
I've just given you a fish, but it won't last long. Soon you will be back asking for another one. So now I'll give you a fishing pole: You need to learn how nesting compositions works in After Effects. You need to take some time to learn the basics of After Effects or else you are going to be here every day asking why this, why that. Everyday asking for a fish. You cannot just download a template and expect to be able to use it. That is an unrealistic expectation. .
Watch this beginner tutorial to learn how to use After Effects: How to add video special effects | Adobe After Effects CC tutorials