How do I bring back my save data from my SD card after replacing board

All the data on your sd is encrypted to your original motherboard, so unless you have or can get the keys to decrypt it, it's gone. If you had CFW on your old board, you can probably get your saves back. This thread has a guide on it, but I do have a few things to add:

• Your boot9.bin and movable.sed might already be in your luma/backups folder if you didn't delete or overwrite them. If you hacked your new motherboard with your old card though, they're most likely overwritten
• DO NOT use the movable.sed you got from bruteforce movable. If you do, you could brick your console
• You probably already have Checkpoint, so if you want you can use that to restore your saves instead of JKSM.
• boot9.bin is the same for every 3ds console, so if you don't have it, you can easily dump it from your new mb
• If you don't have your old movable.sed but you do have your old essential.exefs, you can extract your movable.sed from that with ninfs
• You can get title IDs from 3dsdb.com

If you need any more help, don't hesitate to ask. Good luck!

not really since the motherboard its self is hacked you CAN NOT just expect to swap the motherboard it WILL NOT WORK you have to rehack it since there is homebrew on the system memory you would have to hack it again then swap the .sav files over once youve gotten all the games redownloaded