If you delete a Trainee or a Tasks, the system will automatically delete all of the Training Assignments associated with that Trainee or Task. Rather than doing this, there are some built-in functions that allow you to keep old records, but move them out of the active reports -- out of your daily routine.
Taks are made "inactive", since you still want to see that various employees have completed these tasks. In fact, finding employees who were assigned an inactive task is useful when you want to assign the new, revised, task.
Trainees (or employees) should be archived instead of deleted. This moves their trainee record, and all of their assigned tasks out of the active data. They no longer show up on the Trainees tab, and their assignments no longer show up on the assignments tab. The archived data can be reviewed with a few clicks, and employees that return to work can be "unarchived", which moves them and their history of training assignments back into the active system.
Here is a document that explains how to do it: