He hasn’t decided on a school yet and your are registered for Preview? Preview is not part of the decision making process.
My experience was that the Preview advisor was not necessarily specific to majors or colleges within the university. Meaning, the advisor for my son was not specifically assigned to the college that he intended to pursue. But, I don’t think that is necessary either for the first semester. Also, your son should do research ahead of time to understand what he will have credits for APs/IBs, look at the General Education requirements to see what he will have completed already, and also the courses required for his major. Most majors have a semester-by-semester plan on their websites that he can use as a guideline.
Another thought on the timing or Preview, we scheduled our for the end of the summer so that we would have AP results back prior to preview. That eliminates some variables in the course selection if you know exactly what you will have credits for.