You deleted a document, a version, or an entity, and need it back. What is recoverable depends on how it was removed.
A deleted document version
Deleted versions stay in the document's version history for a retention window before they are purged. Open the document, find the version in history, and use Restore: it becomes the current version again. The history shows the purge deadline next to each deleted version; after that date the file is gone for good.
An archived document
Archiving is fully reversible. Find the document in the library under the Archived filter and unarchive it; nothing was lost.
A removed document slot
Remove document in the slot drawer takes the whole slot away, with every version of its file and its verification history. It cannot be undone. Only slots you added by hand offer it; a slot the checklist put there can only be marked N/A, which is always reversible. The audit trail keeps the record that the removal happened.
A permanently deleted document
Delete permanently (the danger-zone action) removes the document and all its versions for good. It cannot be undone; the confirmation step exists precisely because there is no way back.
An erased or deleted entity
Erasing or permanently deleting an entity cannot be reversed either. If the entity was deleted by mistake, it has to be recreated and its KYB record rebuilt.
Rule of thumb
Prefer Archive when you might need something again; reserve permanent deletion for material that must not come back.