https://www.slab.org.uk/faqs/can-i-delete-my-online-account/
You can delete a draft account by selecting the ‘bin’ icon. If you have submitted your account you will need to reset it to draft before it can be deleted.
You will not be able to delete an account once the status has changed to under assessment or paid. It should be noted that once deleted you will not be able to retrieve it.