By default, you cannot delete scenes. Instead, you archive them - they will always be there in the cloud in case you have regrets and want them back.
If you want to delete a chapter, you first need to archive all the scenes within it.
Archiving a Scene
Plan
In the plan interface, click on the actions menu (three dots) next to the scene title. At the very bottom of the list is the option to archive the scene.
Write
In the write interface, you can also access the action menu, where the archive scene option can be found at the bottom of the list.
Restoring a Scene
There are multiple ways to restore a scene
Press the small folder plus icon next to the new scene button at the bottom of each chapter.
At the bottom of each chapter in the write interface, there is also the option to "add from archive".
You are then taken to an interface that shows any of your deleted scenes. In this interface, you have the option to insert your scene, or delete it. Bear in mind deleting the scene here removes it from your story permanently.
Inserting a scene will append it to the end of the selected chapter. The chapter that you readd the scene to does not have to be the same it was initially deleted from.