How do I remap VC buttons on the 3DS?

Hi there,

I bought my first VC game for 3DS last night. I normally prefer buying physical games, but since the price of Shantae is about $300 on ebay, I prefered the $5 option. Anyway, I can't figure how to remap the buttons, I know how to do it on the Wii U VC, but not on the 3DS. It's very unconfortable to play with B and A in a diamond button setup.

Thanks