Two options for you
1. it is really easy to go to nintendo.com pay them $1 and follow a few easy directions:
https://en-americas-support.nintendo.com/app/topics/detail/p/989/c/269
2. to do it free, you need firmware lower than 8.0.0 OR if you have a firmware greater than 8.0.0 use RCM (if RCM...