To disassemble an item and get scrolls, go to your bag and tap on the item you want to disassemble. Items cost less to disassemble than they do to create in the Workshop. The rarer an item, the more scrolls you get for disassembling it. The number of scrolls that you will get is shown next to the disassembly button. To destroy an item, tap the button.
To prevent you from accidentally disassembling items, the game will ask you to confirm.
Be careful! Items will disappear forever when you disassemble them, and this action cannot be reversed.