Attach the wire or cable to a fish tape or coat hanger using electrical tape and feed it into the hole until it reaches the opening at the other end.
How to drop ethernet from attic.
Poke some cable through one end more than you think you need and leave a short spool at the end slowly walk toward the other plate poke cable through done.
Install brush plates go into attic preferably during a time when temperatures are tolerable walk to one end with your coiled cable in arm.
Run the wire or cable to its destination.
Depending on what the wiring is for this may be go through the drywall to the ceiling for instance for new lighting or be farther down on a wall.
My cable tv is distributed through the attic so it seemed like a good solution to run my home network through there as well.
Cut the holes that the wire will pass through to enter and exit the attic.
When working from an attic space it will be significantly easier to access a wall space on the floor below by working either an interior wall or the exterior wall that is on the gable end of the structure.