The "submenu" he is referring to, it's the icon in the menu at the top which looks like "Cover and Channel" (the 4th icon).
There you can select the origin of the games you want to display.
Wii, GameCube, Channel on Real NAND, Channels on EmuNAND.
If the games are still not displayed, check the path settings.
You need to tell the loader where your games are located (SD or USB).
By default, it's on SD card.
Change the "GameCube Default Folder" to USB : This one is where the dumped games are written by the loader.
Keep the "GameCube SD Folder" to SD : This one is the path used by DIOS MIOS Lite.
DIOS MIOS : display games from default folder only.
DIOS MIOS Lite : Display games from both folders.
If you use DIOS MIOS Lite and launch a game on USB, the loader will ask you to copy the game to SD card first.
If you don't have enough space left on SD, you will see a menu to manage your SD card.
Maybe I should change the default "Main folder" to the first partition on USB, where the games are available to all GameCube launching method.