"You cannot edit your application once it has been submitted. However if you want to change your courses or update your profile you can withdraw the application and send another one, or send the provider a message on your application page detailing the changes you would like to make. Check with the provider before doing this to make sure they are still accepting applications."
From the UCAS website, basically email or phone the university, tell them what happened and ask if it is okay to change. Normally you can just change your course choices but given that the deadline was Tuesday, I would recommend contacting them directly.