In my experience, once you have loosened the fridge enough to pull it forward and gain access to the ice maker fitting buried in the insulation at the top of the fridge, it was just as easy to pull the whole thing out and then replace the tube. Of course this required 2 people, with its height and weight, to lower it to the floor. Once out, we removed the doors to lighten the whole thing for reinstalling. Many installations do not have enough room, either through the outside or inside, to access the top fitting otherwise. (a Dometic RM3662 in my case).
Ours has that heater cable mentioned by Howard and, I suspect, it was the source of the problem in the beginning as the plastic tube itself was no where to be seen when I bought the trailer, the remains were found in each of the fittings though. I think the heater may have been left on by the previous owner with no water in the system. Since we are in Florida and have no need for this option, I have since disconnected the power to it.
One other thing to watch out for: DO NOT loose the metal ferrules in each end of the plastic tube, they are required to prevent the tube collapsing in the fittings and must be reused unless you have new ones!!!
Others have constructed a temporary table-like platform to slide the fridge onto and thus avoid having to lower it to the floor.... perhaps making it a one man operation.
On edit: I should have mentioned that if you are planning on using the plastic tubing again, it can be purchased at Home Depot, Ace Hardware etc and likely cheaper than at an RV dealer.