How to select an object in the hierarchy window during runtime?

I have been working on Easy Build System in Unity where we could place different objects during runtime. After placing the objects, if i come out of the game window and go to the Scene window, I can see that the new prefabs are stored under the name Group (random numbers).

I am doing a project where I want to save those prefabs by the touch of a button. The thing is I dont know how to select the object from hierarchy window by scripts. Has anyone done a similar work to this so that I could refer to it?