What part of “place items on shelf” are you having trouble with?
If you use any one of the many “interactable” examples on this forum, and make the shelf be “interactable,” and create an array of items-on-shelf variable on the shelf actor, this should be straightforward.
So, what you have you tried, and how does it not work?
The first step towards a solution, is to clearly articulate the problem, ideally without any unrelated confounding factors. (This is not just true in game development, this is true in all kinds of engineering!)