How to ungroup objects to its parent?

When i drag the “block1” group I dragged it as a whole. But I what I want to do is when I dropped into the “slot” it I want to ungroup it and get all the “child(cube)” and re-parent it to the “slot”. each cube to each slot. How do I do that? Setting transform.parent = null just removing the “block1” from blocks panel

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drag the cube out and then in to one of slot