If the mother is breastfeeding then maybe the mom can add more fibre to her diet so it gets passed to the baby through breast milk. If the baby is formula fed then you can opt for a formula which is closest to breast milk, like a formula which contains prebiotics. It can help in making stools soft.

Discuss with doctor whether the fm suits the baby or no. Choose an fm with prebiotics that can help soften stool and help build a healthy digestive system.

Breastfeeding is more helpful in this problem. But if breastfeeding is not possible, choose formula milk containing prebiotics. Because prebiotics are good for children's gut. Perhaps the formula milk you are giving is not suitable for the baby. It would be better if you consult your pediatrician.