I agree if we were talking about late 1862, or '63.

But Mr. Friend stated in his question that his Grand uncle, Samuel Friend, was a UNION soldier when he was the Prisoner of War to be exchanged, and that he was being held in a POW Camp in Helena. If a Union Prisoner was being held in Helena then Helena had to have been in Confederate hands. That would had to have been prior to July 12th, 1862.

Now Samuel Friend may have been a Prisoner of war who was exchanged and arrived at Helena after it was occupied by Gen Curtis, but that is not what Mr Friend said.