Hi Akira
I'm not sure how you got into this state - theoretically, it shouldn't happen.
You can go into the database and start deleting rows, but it's very dangerous.
The best suggestion is just to reinstall the database, reimport your processes, and create again the one that is broken. This is only possible if this is a development machine, and you do not have too many workflows already created.
Another option is just to forget about the workflow that isn't working (maybe mark it as deleted), and create it again, with a new name.
If you really want to fix the problem, we could try, but I think it will be a lot of difficulty.
You should perhaps also contact Adobe Support - you should be able to send them your database, and they should be able to reproduce the problem and help you.
Regards,
Howard