FIRE EMBLEM 8 RANDOMIZER INSTALL
Regardless of what option you choose, you will need a 3DS with Luma3DS or a similar CFW with NTR's most recent cheat database as well as a physical or digital copy of Fire Emblem Echoes: Shadows of Valentia (NTR's cheat database will come stock if you choose Luma and no extra install is needed). There are curently 2 methods to do this, one: editing the romfs (is a little tricky but will make your life easier in the long run) and two: using NTR cheats to set classes at Mila altars (is easier to set up, but will be a major pain as time goes on).
If you want to do a randomized run of Fire Emblem Echoes: Shadows of Valentia, you will need a few things for the best experience. Right now, the tool is pretty simple, it generates a table of a character's class progression and gives the option to export the class table, either as a CSV for your reference, or as a JSOn for use with Paragon or other applications which support importing a JSON of the similar format to edit game data. This is a randomization tool to generate a randomized class run of Fire Emblem Echoes: Shadow of Valentia.