It's very, very rare for a trainee to be allowed to switch from Secondary to Primary with the same training provider or vice versa. They have separate requirements, recruitment policies and funding, and you normally have to withdraw from your course and apply afresh through GTTR. What makes you think you are suited to Primary? Do you have extensive experience in primary school and working with that age group? Why didn't you decide between the two phases before applying for Secondary? Remember Primary is even more competitive for entry, and you'll be up against excellent candidates with extensive experience, such as working as TA for years in primary. So there is no guarantee you get a place, and the fact that you've withdrawn from one PGCE will make them wary of you. I still think the best way is to continue with your present course (it's only one year after all), pass it and serve induction, and then look for opportunities for primary teaching. You can gain further experience through supply, and working in transition in secondary school gives you valuable experience with younger pupils and their needs. And your specialist subject is the one that all schools look for, as a core subject.