Oversalted food can be fixed by balancing the salt with sweet or acidic flavors, or diluting the salt. The amount of sweet or acidic ingredients needed to counter an overly salty dish may change the overall flavor into something completely different.
One of the worst mistakes a cook can make is adding too much salt to a dish. Bland dishes are easily fixed with a few additions, but it is harder to de-salt any dish. There are generally two options for countering saltiness in a dish. The cook can add a balancing flavor, such as sweetness or an acid. The flavor choice will depend on the dish. The cook can also dilute the salt with a fat, liquid or solid, also depending on the dish.
Desalting a soup is relatively easy to do. The cook can scoop out about half, or as much as needed, of the broth. Replace this missing liquid with low-salt broth, water, or milk. The soup can be re-heated, tasted and seasoned until the flavor is as desired.
Desalting a solid takes more effort. Salads and mixed grains can have more bulk added to counter the saltiness. For instance, adding more beans to an overly seasoned three bean salad can help to dilute the salt. When adding fresh bulk to a dish, look for bland items such as grains or potatoes.