On the top bar, select "Classes".
Find the ensemble that the student is currently in and click on the "icon with many humans".
Find the student and click on the "three dot icon" on the left of the student.
Select "Transfer enrolment".
Click on the new class to transfer the student into.
Click "Next".
Set the "Start Date" to today or whenever you want the transfer to happen.
Click "Finish".
https://youtu.be/eBLioUbjLuk