What is meant by that is to work him near the barn, then offer to ride away from the barn and go as far as he is comfortable, then stop out there and let him rest, if he will accept it then take him back to the barn. and work more there. Dont' wait unti he takes you back to the barn, you make the turn back to the barn as YOUR decision. So, you might not be away from the barn for very long, but turn him back toward the barn before he loses it.
At the barn, work some more, circles, trotting, backing up, more circles and trotting, then turn away from the barn and repeat, going out in seveal different directions if possible.
Do a searh on the forum for "barn sour" to see what other threads have producesd.
Is your new horse alone? No horses near him , even in sight?