for some reason or another this didnt work for me… the n3ds just refused to accept the microsd…. i followed these instructions, found video versions of these instructions and still no dice… if anyone else is having these problems this link below ended up working out for me in the end!

https://gbatemp.net/threads/how-to-use-a-64gb-micro-sdxc-in-your-sdhc-compliant-flash-cart.335912/