You can delete your prenotification by checking the container and clicking on the ‘cancel container’ button at the bottom. The prenotification is then cancelled at the terminal in question. This sends a cancellation message to the terminal, which will process it so that the prenotification is also ‘Cancelled’ on the terminal side.
It is also possible to detach a prenotification from the visit. Select the container and click on ‘Detach container’ at the bottom. The container can then be found as a status request under the heading ‘Detached’.