Required Reading These instructions will fix your DS mode using TWLFix-3DS-nimhax or TWLFix-CFW . Credits go to MechanicalDragon0687 for creating the apps.
It uninstalls all DS mode system titles and then reinstalls them using Nintendo's Servers by updating the console. Updating not only updates the version, but also repairs broken or missing system titles if the system finds them.
You need either custom firmware or Homebrew Launcher access to launch TWLFix.
Instructions
What You Need The Homebrew Launcher on your HOME menu
The latest release of TWLFix-CFW Instructions Power off your console
Insert your SD card into your computer
Copy TWLFix-CFW.3dsx into the /3ds/ folder on your SD card
Reinsert your SD card into your console
Power on your console
Launch the Homebrew Launcher
Launch TWLFix CFW Edition from the list of homebrew
Press A to begin
When the process is completed, press START to reboot
Update your console by opening System Settings -> Other Settings , then going to the last page and selecting System Update
Updates while using B9S + Luma3DS (what you have) are safe
If the update gives you an error, set both your DNS settings and Proxy settings to Auto
When the process is completed, your DS mode should be working again
What You Need A way to access the Homebrew Launcher
The latest release of TWLFix-3DS-nimhax (direct download) Instructions Power off your console
Insert your SD card into your computer
Copy the TWLFix-3DS folder from the TWLFix-3DS-nimhax .zip into the /3ds/ folder on your SD card
Reinsert your SD card into your console
Power on your console
Open the Homebrew Launcher through your method of choice
Launch TWLFixer from the list of homebrew
Press A to begin
When the process is completed, press START to reboot
Update your console by opening System Settings -> Other Settings , then going to the last page and selecting System Update
If the update gives you an error, set both your DNS settings and Proxy settings to Auto
When the process is completed, your DS mode should be working again
