Placed items can be deleted.
The controls for each device are as follows.
Mobile Ver.
Click the Delete Item button below while the reticle is on the item you wish to delete.
Desktop Ver.
With the reticle on the item to be deleted, press "Q" to delete it.
VR Ver.
When the pointer is over a placed item, press and hold “B”, or when left-handed, press and hold the "Y" button to delete the item.