|Dear Diane ,|
If you open the customer's side of the box they are talking about (gray plastic box with one side bolted down) you'll see at least two modules, each containing a jack (often green) and a pair of screws, red and green next to the jack. Unplug the plugs that are inside the jacks to break the circuits for safety.
What you would need to do then is to put the wires tightened by the top green screw onto the bottom module, green screw, and vise versa and do the same with red. Then plug back the cords you unplugged previously. You should now have line 1 and line 2 swapped.
Dmitri Abaimov, RCDD