Great to have use of MP3tag on Linux but I've found that when trying to change directory when the new folder is selected nothing happens, I then have to drag the files in to the MP3tag window.
It works a little different under Wine compared to Windows: you'd have to select the folder to be opened in the right-side compartment of the selection dialog.
On Windows you can select the new folder on the left-side tree and on the right-side list of folders, but the implementation of Wine behaves a little different. Once you know, you know.