So, you're looking to make another junction table? What's the first one? (That will help me understand what you're trying to do better.)
I've never tried this use case, but I think you would be able to do it using the Repeat Actions option in automations. Find all records in the Course table that are contained in the linked record field in a given Attendee record in the Attendees table. Then add a Repeat Action to your automation and refer to that list. That action would involve creating a new record on the new junction table.
Ok, I've already made another junction table: and manually placed two "attendee's" info into them to get an idea of how I want to the data to appear:
So this table will store/track the attendee to the class. So that we can see a one to one relationship. Granted we can get this data, sort of from the other tables, but for future things like waiting lists, etc, this table will work better.
So an automation will need to be created to "paste" the values into these fields, breaking apart the data that comes from either the junction table or the training calendar one.