There are several ways to make a soup or other liquid-based food items taste lest salty, such as adding starchy food, adding additional liquid and adding competing flavors such as sweet or savory. It is best to add any seasoning, including salt, in moderation, making sure to taste the dish often when adding seasonings.
Starch like a potato, rice or pasta in a soup can absorb the salt form the liquid and, in the case of the potato, the salt can be removed completely. Adding additional liquid, such as dividing the soup into two containers, will help dilute the saltiness. Liquid-based soups can be cooked for a long time, allowing some of the excess liquid to evaporate. Sugar or honey for sweetness, or vinegar or lemon juice for acidity can also make soup taste less salty.