Having had a failed csv import, the help says to press that button.
But of course, no such button exists anywhere I could see. And it then refuses to do anything further.
(I am using the Softaculus version.)
So I guess I need to hack the database. Details as to how would be helpful.
Also, to confirm all users I just
update plxk_user_user set confirmed=1
which seems to work.
To unblacklist someone requires more work, it seems to be stored redundantly in several tables.
I am also experimenting to see what happens if one imports twice, do users end up with duplicate emails? I wish people would not add surrogate keys everywhere (id).