I reproduced the issue that you reported and as the add on has the support level 'Platform support' in the app store, I suggest to file a request with Mendix support to get this fixed in the java code. The code seems to have options for adding new enum values, but not for removing obsolete data from the db.
Erwin is right, raise a support ticket for the App.
Furthernore, this is just one of the side-effects of the flawed enumeration-type that Mendix has defined. Might want to support the improvement of Enumeration in general by upvoting this idea: https://forum.mendix.com/link/ideas/550, that I raised a while ago.