https://3ds.hacks.guide/flashing-ntrboot-(3ds-single-system) rename the open_agb_firm .firm to boot9strap_ntr.firm and pop it in the ntrboot folder. hen run the flasher and enter the key combo. it should work.
does anyone have the source code for this? i was wondering if i could make this into something like the nds forwarder generator https://github.com/MechanicalDragon0687/NDSForwarder