Question about how to perform this function in UE4

In the tutorial he drops the window frame prop onto the surface lip and it pops to the center of the subtracted geometry. No matter what I cannot get it to work! Is there a shortcut key or an option I have to turn on to get this to work? If anyone can enlighten me it would be greatly appreciated as I can see using this down the line and having it be very useful!

Thank you.