QUESTION: How to Copy a Structure?

[Hirnsausen]

Below a gun turret is a cubic structure, and i need to multiply this structure as i want to add more gun turrets. But I am very new to this game, and do not know yet, how to copy a structure. I tried ADD MODE, but that adds a new gun turret and not the desired structure below. Thanks for your help.

[Substep]

https://steamcommunity.com/app/842780/guides/