Intervention only prolongs the agony. I have hens which are very fiesty and will take almost anything on. Some of them have taken on cocks and given a good account of themselves...but only for a short while. They have to be allowed to sort it out, otherwise nothing is resolved.
The fact that your cockerel is young may complicate matters. If the hen bests him, he will be cowed and may take a long time to regain his confidence. Keeping him on his own for a few weeks, in sight of the others, will allow him to mature and, when he is reintroduced to the flock, he should be able to exert his dominance.
The trouble is, the hens know exactly what he is and, if they see him as an immature lout, they will treat him as such. In a few weeks they will see him as something completely different. His confidence will have grown, and he will be able to stand up for himself better. It's all about timing when introducing young males to older hens.