If you want to remove the ownership of a thing from a user, a procedure called unlink thing is necessary which allows the platform to know that the user is no longer the owner of the thing.
In order to unlink the thing the user must be logged in and the thing must be activated and previously linked.
Unlink thing from an app with the thing ID
The thing lD could be retrieved from the GET:/me/things or GET:/me/resources
After this, the app does not have access to the user's thing data anymore.