I'm trying to create a training course waitlist. Are those who sign up able to remove themselves from the list once they've been able to attend the co

The form submissions can be deleted only by the form owners.

You can include an Edit Link in the email they would receive when they fill the form.
How to Let Users Update Their Form Submissions at a Later Date

To clarify, once again, this only means that the users can Edit the form at a later date and not Delete their submission.