The White House documents being declassified is hearsay.
Trump's White House Counsel, Pat Cippolone, has made no such claim.
In any event, under security classification rules, a classification marking on a document has to be treated as valid and binding unless and until a subsequent marking replaces it. Appropriate government staffers would have needed to cross out the classification markings in the headers and footers, and stamped 'declassified' on the record noting when it was declassified, by whom and under what authority.
Trump had, apparently, absconded with documents that are required to be turned over to the National Archives.
Trump can reveal the warrant and what was found and confiscated.
His hiding that information appears to be in his interests as he sees it.