Switch, Add and Remove Flaps
In order to glue the split edges together in the real world, it's necessary to place a flap on one side. You can choose which side the flap should be placed on by using the Flap Tool. First make sure you are in Switch mode, otherwise click the button in the Inspector. Then click a flap to move it to another side or click an edge to move the flap on another side to this side.
In some special cases, you may want to add an additional flap or remove a flap that should exist. To do so, switch to Add/Remove mode by clicking the button in the Inspector. Then click an edge without flap to add one or click a flap to remove it. The added flaps are marked with a green dot and the removed flaps with a red one. To remove multiple flaps at once, drag from an empty area to make a selection box. All flaps touched by the box will be removed. To add multiple flaps at once, hold down the option key while dragging.Reshape Flaps Styling