I installed collective.folderishtypes with Plone 5.2.3.
How to convert all existing objects (supported by the addon) to folderish objects?
The documentation seems to be for an older version of Plone with ATContentType.
If you use Dexterity, I don't think you have to migrate anything. You can just change the 'base class' of your content type to folderish.
Search this site (community.plone), I think there are some answers