My little one is almost 4months old, she can flip from back to tummy, but she can't support herself when we put her in sitting position. Just a guide, bout how old does your baby manage to sit unsupported?
My boy able to sit up with support about 5 months. And before he turned 6 months, he was able to sit up without support. Dont worry mummy, they will do it on their own once they ate strong enough and is ready to do it.