Try the following to remove indentations in a carpet where furniture legs used to sit.
To remove carpet indentations (sometimes called memory from an object's weight on the carpet for a long time), hold an iron over the area and apply the steam setting to full. Keep the iron 2-4 inches away from the carpet to avoid direct contact. The goal is to get the hot steam to reset the carpet and gradually remove the furniture indentation in the carpet. Once you have applied the steam for several minutes, try raking the carpet with your fingers once it cools to a safe termperature to touch. Repeat the process several times until the carpet is smooth and level.