To help relieve constipation in a 7-month-old baby, you can try increasing the frequency of feedings to every 3 hours, day and night. You can also offer small amounts of water during meals and gently massage the baby's belly in a clockwise direction. Another helpful tip is to encourage the baby to move their legs in a cycling motion while lying on their back. If these methods do not work within 2 or 3 days, you may consider using a gentle laxative after consulting with a doctor. It is important to note that laxatives should only be used for an extended period of time if recommended by a healthcare professional to avoid masking more serious underlying issues.