Cases are intentionally hard to delete in Nook – for historical and reporting reasons it is much better to archive them. If you DO need to delete a case (for example, if a duplicate has been created), one way to do this is within Reporting.
Go to a Project report for the project the case is in.
Run a Case Report (optionally adding filters to help find the case record you’re looking for)
Find the case and check the checkbox in the leftmost column of the table.
Go to Action > Delete Energy Advice Cases.