How can I insert scenes/chapters between two that already written?

As of November 2024, you cannot currently insert a chapter or scene above another in the write interface. It is a planned feature, however, that will come to Novelcrafter soon.

To work around this, you will need to go to the plan view, where you can easily move about chapters and scenes once they have been made.

You can request the feature here, by ‘upvoting’ it.