In trying to learn how to use your app, I can save a file, but I can not control to where it saves.
Normally on a MAC, one can go to the “save file” menu and press the “options” key which brings up the “save as” menu item. On your app, it brings up an option to “close all” but the “close” menu is not even highlighted. Maybe this is a bug.
I did find that you can use the “move” menu to move it to another directory, and the app remembers (I think) the last directory you used.