Hi, I deferred a few of my admission offers in 2020. My experience with that was rather simple, possibly due to the pandemic. I emailed the admissions office regarding the offer, with my request and reasons for deferral. My story was pretty straight-forward -
I was incredibly grateful for the offer, but the pandemic had thrown a wrench in my plans.
Explained my situation - There was no way I would be able to complete my undergrad in time to join the university. That meant I wouldn't be able to procure the necessary documents in time, or even travel if/when restrictions were lifted.
Requested for the deferral, and thanked them for their time (they did seem to have a lot on their hands, after all).
Some of them responded positively and got it confirmed within the week. When there was no response, I got in touch with my program department as well. In most cases, they were very helpful and redirected me to reach out to the right contacts. In some cases, I was also given a form to fill out the details regarding my request.
Personally, I think it was important for me to highlight how grateful and thrilled I was to receive the offer, and how external factors were impacting my decision.
The unfortunate part of asking for a deferral is this - your request might not be accepted, no matter how valid the reasoning may be. Out of the 6+ colleges I emailed, only 3-4 were able to defer my offer. A few others could only suggest to reapply next year. However, it was better than receiving no response at all (which did happen as well).
I think there are people here who'd answer more specifically regarding your course and university, but I hope this helps a bit