Use the Decrypt9 A9LH payload for that! It gives you the option to extract AGBSave. You just have to launch the game you want to backup the save of first, then turn off your connsole, boot into Decrypt9, and I'm not sure where exactly it is, but there will be an option to backup agbsave or something like that. It'll backup the save to your files9 folder on your SD card.