You're looking for information on backing up and downloading your Wii's NAND data. Here's some relevant information:
The following essay examines the technical, legal, and preservationist implications of Wii NAND backup downloads within the homebrew community. Wii Nand Backup Download
: Press the Home button and select "Launch BootMii." You're looking for information on backing up and
Copy your saved nand.bin and keys.bin back to the root of your SD card. Insert the card into the bricked Wii and power it on. Wii Nand Backup Download