Thank you for reaching out to the Community for assistance.
Each school has a different process of registration and can provide the best steps to move forward when enrolling students. You will need to contact the school or district directly to ask when and how you would be able to enroll your child and inquire about the selection of base school.
The PowerSchool Community is a great resource if you have any difficulties completing fields within the enrollment form. You can check out the FAQs related to the enrollment process here.