Hi @MB_10034486
If you log in as an administrator why do you not use the delete button from the table menu?
What error do you see if you use it?

I guess that you use a load from file functionality without specify a user so you can not delete it. as a system
This is a consequence of your action.
So the resolution is: delete it from a database or change the owner in the database. There is no UI operation that can help.
I have one advice. If you use load from file and you do not know all consequences really use a backup on your developer(test) system before you do it in a production. . You can revert the backup when ever you need.
PetrH