Open a NDS game file or a BIN file exported from Forwarder3DS, pressing the folder icon button in the upper-right corner.

Edit whatever you want to edit. Change between titles and icons options using the menu button in the upper-left corner.

Press the floppy disk icon button in the Action Bar for saving your changes. You can whether to Overwrite the opened file

(this will work on both NDS and BIN files)

, or Save as...

(which currently works only for exporting the BIN files, you'll need to backup your NDS file before saving the changes)

.