Only show own courses when adding classes

Hello, First of, thank you for this great product. I have a use case where a teacher can create a class but is allowed only to add the courses he created. By default when creating a class all courses are shown. How can we restrict the select to only show the courses created by the current user. I know object type Class has an entity reference to Course (opigno_class_courses) but how can we enforce the owner restriction? Thanks in advance, Johnny