3DS format to DSi

1. Download this release of ctrtool. (https://github.com/ThisIsDaAccount/Project_CTR/releases/download/1/ctrtool.rar)
2. Extract ctrtool into its own folder and put your .cia file in that folder. Rename your .cia file to "dsiware.cia".
3. Run extract.bat. You should get two files, one of which will have a size of 0 kb. Delete the 0 kb file.
4. Keep the other file that is not 0kb and continue with the guide.


(from https://gbatemp.net/threads/gbatemp-dsi-modding-help-thread-and-guide.481118/)