So, looking at conversations on the Github, it seems the import button literally isn't implemented.
Shame, because this tool actually solved an issue I was having with texture editing for clothing. (Which areas render as skin and clothing is determined by an image file Ohana can't detect.)
But I can't actually ACT on this because Ohana can't see the file, so it can't replace the file... And meanwhile Spica can see the file but can't replace it anyway.