Thank you guys.
So to install it on my CFW old 3DS, I need to
Extract/overwrite the _nds folder, and boot.nds file, to the SD card root.
For DSi CFW users, put title from CFW - SDNAND root folder, onto the SD card root.
On 3DS, install the two CIAs in the cia folder.
And skip the 2nd step...