While other greens wilt to a delicate texture after just a few minutes in hot water, collards are made of sterner stuff. Their robust leaves stand up to extended slow cooking, retaining their shape and texture just as well as dense root vegetables. This means they can be paired with flavorful, long-cooking meats such as ham hocks, which infuse the greens with a rich flavor. Those meats are also cured and highly salted, so occasionally you might find that your collards have become too salty to enjoy. That's irritating, but easily remedied.
Addition by Subtraction ...
It was water that conveyed the salt into your collards, and water can strip it back out again. Rinse your greens in hot water to correct minor over-salting, or transfer them from the original "pot-likker" to a saucepan of fresh, boiling water. After a few minutes of boiling, the greens' salt level should be reduced to something more tolerable. If you enjoy the pot-likker, Southern style, as part of the meal in its own right, ladle some out into a measuring cup and dilute it with the collards' fresh boiling water until it tastes as it should.
... Or Compensation by Distraction
If the greens are mildly but not overwhelmingly over-salted, they might still be usable with a minor tweak or two. For example, a splash of lemon juice or mild vinegar brightens the collards' flavor and helps mask their saltiness. Another alternative is to match them with foods bland enough to compensate for their heavy seasoning. Plain boiled or mashed potatoes, rice, cornbread or grits eaten with the greens -- as they often would be, anyway -- can blunt the salt's impact and reduce it to a palatable level.