The short answer is you don't!
Once post/programme details have been made available for selection they will remain in this status until the deadline is reached.
When you access your preferences on Oriel, you can arrange them as you see fit; when you have finished, click 'save' to retain the posts in the particular order/arrangement you have given them.
However, they do not need to be submitted. Posts will remain in the order/arrangement you have saved up until either preferences are closed, or until you change the order/arrangement - which you can do at any point, and as many times as you like, up until the preferences deadline for that application.
In terms of submitting preferences; essentially, once the preferencing function is closed, your posts will be 'submitted' in the order/arrangement they are saved at that point.
Please see the Medical Specialty Recruitment Applicant Handbook Oriel - Resource bank for more information.