How to edit "from where?" list?

I know how to change the content of the "from where?" list. But I made some errors in specifying the places, and I would like to remove them from the list. In Power Edit I can select all books wrongly tagged and I suppose that if I change them the offending entries will be removed, but I don't know how to do it in a single step (and searching on wiki pages does not work :-( )

That I'm aware, From Where is an individual edit situation, not something that can be mass edited.
If you linked to a venue for your From Where, and it isn't claimed by an owner, you can correct the local entry to get the right name, but beware of edit wars.
If you put in free text, you'll have to go to each one.

it is free text ("LT Early Adopters" instead of "LT Early Reviewers")... I'll change them one by one.