Had my baby lay on his belly a lot of times to help but maybe ask doctor
Maybe try fillin up one of the baby syringes wit soap and warm water and usin the syringe to push that warm water and soap up their booty It’s what worked for me when my youngest was constipated as a baby
Diluted apple juice or prune juice
If you are bottle feeding try and use ready made baby milk if they have the same formula make your already using. I used to give my baby 2 bottles a day and that helped.
Gripe water
A round of probiotics helped our little one!
Warm water first thing in morning. Maintain gap between meals. Freshly cur Apple pieces or apple juice. For initial few days take care what he eats
Ask your doctor for Movicol