How to use dosbox libretro?

I searched everywhere and asked on IRC and discord servers, I have no idea how to run DOSBox games using the DOSBox libretto

I put “Retroarch” folder on the root of the sd, and then I install the .cia, after that, I launch retroarch, and I put “start” on the top, and try to load a DOSBox game but it doesn’t do anything. what am I missing? help ! thank you

new 3ds