My baby is 6 month old but she couldn't roll over.. she's trying but I think her head is too heavy

A. Keep your child on the tummy give more of tummy time which will be very helpful for the child along with that also I’m going to advise you that the child would learn to roll over with that and encourage your child if you feel the head is very heavy then check with the doctor because the head of the child has to be proportion to the body