In any list view, you can use the "slow" double click to edit.
This function does not work in that part of the interface, which is the problem. Hovering the mouse over that area shows a cycling display of tag information.
also Alt-Enter brings up the tag interface on a file
It's not a tagging issue. I can have two distinct albums in the interface shown in the screenshot while within all of the files are tagged as "The National".
The only solution I've found to combine them is to drag the incorrect version of the band onto the correct version over on the sidebar on the left. Unfortunately, as I have the bands sorted by "date imported", this means I have no idea where within that large list the correct band is.