There's a few ways to import a trainer, depending in part on the game you're importing from. Regardless of where they're from though, there's a way to move them over.

Moving Trainers over from Eclipse or Crater simply requires a valid document of their pokemon / items / levels and coins.

Reach out to me if you want to import a character, as i have discovered it is so much faster if I do it directly in the server -- I'd be more than happy to help.