If the line is just over-wrapped or pulled down through the layers and the drum otherwise turns freely, just pull harder on the line. Or connect the rope to something and back away from it after insuring the winch is in free-spool mode.
Remember that a winch rope should not be allowed to be wound on too loosely, it should be re-wound onto the drum evenly under load. I run my winch line out until only the bottom layer is left on the drum. After attaching the winch hook to something solid, I pull my parking brake handle up a few clicks and then use the winch to pull the Jeep forward toward what the line is connected to, winding it evenly onto the drum as I go.