Marking a logbook attached to a logbook will allow you to delete the logbook from settings.
If you are unable to mark a Logbook that's attached to a ripple as out of use you will need to make sure that the Logbook is not being used within any steps on any ripple on your site.
📌Note: You either need admin access or access rights to logbooks and ripple to make this change.
To do this you will need to click into the ripple that the Logbook is attached to click into the Logbook either Delete the step or click the Pencil icon and assign a different logbook.