RxTools doesn't support N3ds as of now, there are other CFWs like reiNAND/Cakes etc, for N3ds.
https://gbatemp.net/threads/tutoria...luding-emunand-coldboot-cia-installer.405589/ >>> This will help you
Also, a simple google search would've been enough. Try googling first before making a thread x_x
EDIT: rxTools does support N3ds(RxTools 3.0 Beta), but it is still beta, and in testing, so I Cakes/reiNAND would be better for now, atleast.