For more info, read the GBAtemp page: https://gbatemp.net/threads/cube-creator-3d-minecraft-conversion-mod.679635/#post-10828614
To install on 3DS, place the romfs folder in this directory: [SD card root]\luma\titles\0004000000151100. If the title ID (0004000000151100) folder doesn't exist, create it. Make sure your 3DS is modded with Luma before installing! This mod should work fine on both old and new 3DS devices.