[Setup] Trying to remove Invalid step handlers

[Rob Gregory]

Hello everyone,

I am relatively new to the Plone world, having done light admin work
on it for about a year, and really only now moving into the "heavy
lifting" of moving instances, fixing broken products, etc.
Currently, I am wrestling with the migration of a 3.3.5 instance to a
4.1 instance. The 3.3.5 had a product custom built by my predecessor,
which I removed through the portal_quickinstaller. Now that I have
moved the Data.fs into a 4.1 instance and upgraded the site, I am
attempting to remove invalid step handlers related to the custom
product.
However, when I select any item in portal_setup/manage_stepRegistry,
then click "Delete selected steps", I only get a "This page does not
seem to exist..." message.
Checking the log does not reveal anything about this. Is there some
way to force the ZMI to behave, or do I have to do this through the
debug console?

If I need to plunge into debug, is there a guide somewhere I can use
to help me figure out what to work with? I am working on a test copy,
so I'm not afraid of nuking my ZODB if I accidentally commit the wrong
thing while I'm in there. Any help would be appreciated. Thanks!