If you've invited a trainee and want to cancel the invitation because you've made an error, or the person has left and you want to invite someone else, you can. Note: this is different from deleting a trainee that you've added using the bulk upload or the add trainee form, this only works for pending invitations via email.
From the Trainees and courses page, choose Options > Pending invitations, or click on any of the numbers in the Pending invitations column.
Click Options > Delete next to the trainee whose invitation you want to cancel.
You'll then need to confirm the deletion.