You can use the Chopping Board booster to unmerge items on your game board. Level 1 Chopping Board allows you to unmerge regular items, and Level 2 Quality Chopping Board also allows you to unmerge Generators!

You can use the Chopping Board by double-tapping on it. Then, you need to tap the item you want to unmerge and tap the green checkmark button in order to confirm the unmerge.