Adding potatoes to an oversalted dish can help reduce the perceived saltiness. Potatoes absorb some of the excess salt and liquid, diluting the overall salt concentration.
Potatoes are starchy vegetables that act like sponges in a dish. When you add raw or partially cooked potatoes to an oversalted dish, they absorb some of the surrounding liquid, including the salty broth or sauce. This absorption effectively dilutes the salt concentration in the remaining liquid, making the dish taste less salty. The potatoes themselves will become saltier, but the overall balance of the dish should improve. You can then remove the potatoes before serving, or leave them in as part of the dish, depending on your preference. The amount of potato needed depends on the volume of the dish and the severity of the oversalted condition. Start with a small amount and taste as you go, adding more if needed.
Don't overcook the potatoes while they're absorbing the salt. Partially cook them beforehand or add them in larger chunks so they don't disintegrate and make the dish starchy.