To help alleviate nasal congestion in a 6-month-old baby, you can try using saline solution to clean their nose. Avoid using nasal sprays with medication, as they can have more side effects and offer minimal benefits. You can also try having the baby lie on their back and gently clean the edges of their nostrils with a wet tissue, followed by using a nasal aspirator if needed. Encouraging the baby to breastfeed or use a pacifier can help them swallow any excess mucus. Applying non-medicated ointment like Vaseline around the nose can help soothe irritated skin. Keeping the room temperature around 68°F (20°C) and avoiding exposure to respiratory irritants like secondhand smoke and dust can also help relieve nasal congestion.