Essentially (for example) the trader has a position that makes money if LIBOR goes down, so he calls the LIBOR submitter at his bank or someone he knows through

Essentially (for example) the trader has a position that makes money if LIBOR goes down, so he calls the LIBOR submitter at his bank or someone he knows through contacts at another bank and says "hey it would be nice if your 3 month LIBOR could go from .7% to .65%", and the submitters who were themselves often low level functionaries just did it as a favor. Though they could only move it within bank guidelines so the profits made were not huge in any case.