Skull depression in newborns is a common condition, which is often called "fetal head depression" or "forceps depression". This happens during childbirth because of pressure on the head. In most cases, it is harmless and will recover itself within a few weeks.

However, if the sag is obvious or lasts for a long time, some measures may need to be taken to improve it. Here are some possible ways:

1. Massage your baby more: Massage your baby's head gently, which can promote blood circulation and lymphatic flow, and help to reduce the pressure and swelling of the head.

2. Let the baby exercise more: Let the baby do more appropriate exercise, such as push-ups, looking up, etc. Can help strengthen the strength of the neck muscles, thus reducing the pressure on the head.

3. Pay attention to sleeping posture: Try to keep your baby sleeping in supine position and avoid sleeping in lateral position or prone position, which can reduce the pressure and friction on the head.

4. Use special pillows: Some special pillows can help support the baby's head and reduce the pressure and depression on the head. But it is best to consult a doctor before using it.

It should be noted that if the baby's head droops seriously or for a long time, it is recommended to seek medical advice in time to eliminate other potential problems.