This guide is intended for consoles that are suffering from hardware failure and can no longer function normally. If your 3DS can still run GodMode9 , see GodeMode9 Usage instead.
What You Need
Section 1 Prep Work
Power off your console
Insert your SD card into your computer
Rename boot.firm to luma.firm, if it exists
Copy 3ds_essential_dumper.firm to the root of your SD card
Rename 3ds_essential_dumper.firm to boot.firm
Reinsert your SD card into your console
Section II: 3ds_essential_dumper
Ensure your SD card has at least 1.3GB of free space if you plan on doing a NAND backup, and that it is formatted to FAT32 using our guide
Power on your console
When the Power and Notification LEDs flash red, press A to dump the NAND
If you do not need a NAND dump from the console, press B instead
Wait for your console to turn off. If dumping the NAND, this can take over 30 minutes to an hour
Insert your SD card into your computer
Your dumped files will be in the /edump/ folder on the SD card 
