You should contact your lecturer or course leader who deals with your unit. It is best to email them an explanation of the problem in advance of the deadline. You should take screenshots of the problem as this will demonstrate your ability and willingness to submit the work on time.
It is a good idea to at least check that the link is there well in advance of the deadline, if not submit, because that will give the tutor time to resolve the problem, and if you need to make a Mitigating Circumstances claim or appeal, you can prove you reported the problem in good time.
The academic who marks the work is the one responsible for setting up the link, so if you are unable to contact them prior to the deadline the best solution is to make them aware by email. Please note that while the SiD team will advise you as best possible about your options, we cannot set up links for you.
You should also bear in mind that if your submission involves a hard copy, both copies must be submitted before the deadline.