It can be released on his orders. He is the ultimate classification authority, DOJ works for him. He’s trying to throw congress a bone to do the right thing, but he is the releasing authority.
Actually he's not. The memo is House Permanent Select Committee on Intelligence work product. The man with the final say so over its release Devin Nunes, Committee chair. He can sit on it or release it with or without the President's approval. However, since a lot of the sourcing for the memo is from classified Administration sources, he wants Trump's approval before he releases it.