(but there is a process to go through when declassifying documents and there is no evidence that Trump took those steps while he was in office)
What evidence should be presented specifically?
There is a process for the President’s subordinates. An Air Force officer for example may decide something is ok to be declassified and there is a process he must follow.
The President is the final arbiter of what is and what is not classified. He does NOT have to follow a process. Nobody can overrule his decision. He does not have to prove anything to anyone else to declassify something, and he does not have to obtain permission from anyone.