Deleting a data subject request in Sypher isn't final right away. Deleted DSRs are kept for 30 days, and during that time you can restore any of them with a single click, whatever the reason it was deleted.
Go to Project Settings → Deleted Items and open the Data subject requests tab. You'll see every deleted request with its reference number and the date and time it was deleted. From there you can:
After 30 days, deleted requests are permanently removed, in line with data minimisation. Restoring is available to users who have the right to manage and assign DSRs.
Deleted Items has two more tabs, Mapping and Security incidents, which work the same way.