Good Day! I am sorry to hear that you are facing an inconvenience due to this and understand your concern. Once a form is submitted PowerSchool can't make any changes to it. I recommend reaching out directly to the school district's enrollment section as they would be able to disassociate your child with their district.
For future reference, here are the most commonly asked questions by Enrollment Family users.
PS: Wishing a great school year to your child.