Reasure Child that he is Safe.
Don't just plunck child down and walk away. This gives feeling of rapture and activates lower brain fear system.
Make crib a familiar cosy place.
Give lots of Hugs and cuddles in the day and before bed.
Use the senses to help ground child and help him feel safe and comfortable:
Sound – use white noise, the sound of mother's voice (or father's), Consider using a recording of parents voice with messages such as: “You are safe, I love you” or storries or songs. Recording and white noise can be left on all night long.
Smell – Include items in the bed that smell like Mom/Dad or breastmilk. This helps child develop an emotional association.
Lovey/Blankie – a soft transitional object for child to cuddle up with. Item can smell like parent.
Consider massage as part of your bedtime routine.