It is known that crooked or flattened skulls occur because babies lay in a favoured position for too long. The baby's skull is still weak, so one side of the head can end up flatter than the other.
In addition to a skewed head, a laying preference can have other consequences; it may cause babies to move asymmetrically or unilaterally, causing development barriers.
With simple changes to behaviour, you can stimulate the baby to more actively favour the non-favoured side. Here are some examples.
If you bottle feed, keep him firm so that he has to turn to the non-favoured side to see you. Make sure both arms are forward.
Or put him right in front of you, so his head stays in the middle.
In the cot on their back
In the cot on their stomach
In the cot on his side
On your lap
From angelababy In Q&A
From daisyrowley In Pregnancy