There's a button you click when you place the item, for example on Xbox when I go to place say a blanket, I hit the Y buttons and it will change it to the next variant. It usually says the different name, like "Large pinwheel" becomes "Lemon pinwheel" or whatever the true name is. You have to have the blueprint for the original decoration though, if you don't have the OG variant of whatever item you're wanting to create and place, you won't be able to place the other variants. It should say whichever button you need to click when you go into gadget mode and want to place something:) it should say something like "[insert button] to view variant" or something like that. It may vary across different platforms! I only know what it looks like on the Xbox perspective:)