Vitamin C is not a collagen source. Rather, it’s a substance that’s necessary in the body’s production of collagen. Your cells use Vitamin C to make procollagen, a precursor of the collagen fibrils that make up the connective tissues of your penis.
There is an ongoing debate as to whether Vitamin C helps or hinders PE. It may help in that it allows new collagen to be laid down; it may hurt by excessively strengthening the tissues of the penis and making them resistant to extension.
Direct ingestion of collagen is not especially helpful. First, collagen is a fairly large molecule that probably does not survive the digestion process. Second, even if it were to survive, there is no way to deliver the collagen directly to the locations in the penis where it is needed. Collagen is not delivered to the connective tissues via the blood stream. Rather, it is manufactured locally by cells called fibroblasts, which are interspersed among the fibers in the connective tissue.
Collagen is probably a good source of amino acids, which the cells use as building blocks to construct collagen. But I doubt eating pure collagen would be any better in promoting collagen production than just eating a balanced diet that includes meat.