Consider that, in order to dump save files, you need access to Slot-1, so DSiWare exploit isn't enought, you have to install Unlaunch (following ALL the guide linked by @BlackShark).
Well there is this (haven't used it yet though) https://gbatemp.net/threads/release-ndsi-savedumper.515520/
Running homebrew on DSi is easy as well nowadays https://dsi.cfw.guide/
Hey all, sorry I've been unavailable for a while. Someone suggested I start a discord server so it would be easier to communicate and have a central hub for NGC/Wii ROM hacking updates. Here's the link if anyone wants to learn, get support, ask questions or have a chat: https://discord.gg/xCPjjnv