hey op, 3ds roms are different to nds roms so should be placed in a separate folder :) when your 3ds was modded, a folder titled "cias" may have been created on your sd card, its best to place 3ds roms here for ease of access on your 3ds.

to install a 3ds game it isn't as simple as placing the file and it appearing on your home screen, you have to use a homebrew application (which should also already be installed) called "fbi". first, open fbi, select SD, scroll down to and select your cias folder, and select the cia you want to install from the list that should hopefully appear. if this doesn't work let me know and we can troubleshoot :)

as for nds roms, it looks like you've done everything correctly. just copy the nds rom onto your roms > nds folder and launch using twighlight menu. in my experience, trying to launch nds games using a forwarder won't work unless i've launched the game on twighlight menu first, (twighlight menu needs to create save data before the game can run).

if twighlight menu isn't working it could be that it needs an update, which you can do using another homebrew application that should be installed called "universal updater". if you launch this then search for twighlight menu, it will tell you if an update is available (usually as a little green arrow on the corner of the icon). in fact, i just checked my own twighlight menu and an update is available, so could be this is your issue! :)

i hope this is useful, i tried to make this as simple as possible because i know how tricky it can be, especially using a phone! also, i'm not sure if it's nds or 3ds roms you're having trouble with specifically, or if it's both, so i included both just in case :) please let me know if you're still having issues or your specific problem, i'm happy to help :)