Back-up sysNAND if you didn't already (look that up)
Put FixBlueCard.CIA (or whatever it's called) onto your internal SD Card.
Get DevMenu.3ds or BigBlueMenu.3ds (look those up)
Use Gateway to boot into sysNAND (look that up)
Launch DevMenu or BigBlueMenu, navigate to the second tab and install the FixBlueCard.CIA