How do I transfer data from the SD card to the console

At the risk of sounding like an idiot I dug up my old 3DS as I wanted to play pokemon moon again, have recenly been told I can actually use it as an mp3 player and am super happy about that however, the SD card does not have enough storage for music so I want to transfer all the data on it to the console so I can put in a new one, I have looked through the settings and Data Management but cannot see where to do this maybe I'm being an idiot tho